This article will show you how to update your operating system on a Macintosh computer.
Latest Update Available: macOS 10.12.2 (Sierra)
NOTE: The latest operating systems require 2GB of RAM, but that is just how much the system resources need. To run any applications on top of that, you should have at least 4GB. If you run more than a few applications at once, or any memory-intense applications, you should have at least 8GB. Sources to purchase additional RAM include crucial.com and macsales.com.
If you are not sure what year/era your Mac is from, click on the Apple menu which appears in the upper left of your screen, then click About this Mac. You can either click More Info, which will open System Information, or you can click on the gray text that says "Version" twice. Either method should display the serial number. Once you have found the serial number, enter it at http://selfsolve.apple.com/agreementWarrantyDynamic.do.
Mac OS X 10.5.8 is the latest version if you have a computer with a Power PC processor (that would be pre-2006).
Versions up to 10.6 also require a DVD drive, as these versions are only available on disk. Starting at version 10.7 Lion, upgrades are available via the Mac App Store. 10.7 is available on a USB stick as well.
Upgrading from Pre-Snow Leopard to Post-Snow Leopard
Apple has announced that users interested in upgrading to Lion (10.7) or later can do so from Snow Leopard (10.6) using the Mac App Store (10.6.6 or later required for the Mac App Store) without having to purchase or download the intermediate versions. Therefore, if you have Leopard (10.5) or earlier, and have a Mountain Lion compatible Mac, you will have to upgrade to Snow Leopard first to get Mountain Lion or later, and you can skip Lion. To get Snow Leopard, order it on disk: http://store.apple.com/us/product/MC573/mac-os-x-106-snow-leopard. The disk at the above link ships with version 10.6.3. You will need to run a software update to get 10.6.8, the latest version of 10.6. You can also choose to run this Combo Updater (you still need 10.6.x for the updater to work). Updating to 10.6.8 is necessary if you intend to install a newer version afterward, and a good idea anyway. It will give you access to the Mac App Store. Once you have 10.6.8, you can upgrade straight to Lion, Mountain Lion, or Yosemite.
NOTE: Do you Need Snow Leopard (10.6), Lion (10.7) or Mountain Lion (10.8)?
With the release of Mavericks, Mountain Lion was removed from the Mac App Store, and the same thing happened to Lion when Mountain Lion was released. You can still order it, however, by ordering a download code from the Apple Online Store (see "Buying a New Version of Mac OS" below). For Lion or Mountain Lion, you can order a code to enter in the App Store for $19.99 (again, a minimum of Snow Leopard 10.6.6 is needed to get the Mac App Store). Snow Leopard is only available on disk (linked above). Every OS from Mavericks (10.9) onward has been completely removed when a subsequent upgrade is released, and is no longer available.
What Version do I Currently Have?
Just like described earlier, click on the Apple menu to begin, then hit About this Mac. You should see a display like below.
Below this display is a Software Update button. This is another way to access the software update. You can also click on More Info to find information about graphics, processors, serial number, and software.
Buying a New Version of Mac OS
There is a difference between "updating" and "upgrading." Updating is when a newer version of your current software is available (for example, going from Mac OS 10.7 to 10.7.1). Updates can be found by doing a Software Update, described above. Upgrading is buying an entirely newer and better software version of Mac OS (for example, Mac OS 10.6 to 10.7). So if you see "Your software is up to date," then that means that your version of Mac OS X is up to date. If you don't know which operating system you have, please refer to the "What Version do I Currently Have?" section above. Then check below to see the name of your version of Mac OS X.
If you have an older computer, your hardware may not be compatible with the latest and greatest, but you may still be able to upgrade to a new version. Versions up until 10.6 (Snow Leopard) can be purchased on a disc. Version 10.7 and later can be downloaded as a digital copy from the Mac App Store. The Mac App Store requires Snow Leopard, running 10.6.6 or later. If you have Snow Leopard but do not have the Mac App Store, you can check for software updates, and the latest version (10.6.8) should have the Mac App Store.
Mac OS X Snow Leopard requires 1GB of RAM, and all later versions of macOS require 2GB of RAM. If your Mac meets all other requirements for a macOS upgrade but does not have enough RAM, you can probably upgrade to more RAM. Two good sources (there are more) to buy RAM are Crucial - http://www.crucial.com/usa/en/apple-memory, and OWC - https://eshop.macsales.com. Note that, for smooth performance, you should probably have at least 4GB of RAM installed if your Mac supports it. Below is a chart of all modern macOS versions, and the amount of RAM we recommend.
Add Software Update to your Dock
Note that the below will only work on Mac OS X Lion (10.7) or earlier. In 10.8, Software Update redirects to the Updates tab of the Mac App Store. If you add the icon to your dock prior to upgrading to Mountain Lion, this will still work and it will retain the shortcut in Mountain Lion.
You can check for updates a lot quicker by adding the Software Update icon to your dock. Software Updates can not only check for operating system updates, but also for application updates such as iPhoto, iMovie, Keynote, Pages, printer drivers, etc. So first, go to the Apple menu in the upper left and click Software Update...
The Software Update icon should appear in your dock. But when the application is quit, the icon disappears. You want to keep it in the dock so that you can access it with a single click any time and have it check for updates. To do so, hover over the Software Update icon, and do a right click by holding the control key while clicking. Then click on Options.
From there, you should see an option titled "Keep in Dock." Click on that, and a check mark should appear next to it. Now, when the application is quit, the Software Update icon should remain in your dock. You only need to click on it again and Software Update will launch. Note that the "Keep in Dock" option will work on any application, not just Software Update.
There are many ways to access Software Update on the Mac, and Mac OS makes it easy to stay up-to-date. Use any of the above methods to check for software updates periodically. You can set it up to check automatically under System Preferences > Software Update (in the System category) > Scheduled Check, and then select the box "Check for Updates:" and you can choose daily, weekly or monthly.
See Will My Applications Work when I Upgrade macOS? for more information.
There are a number of users who state that they cannot open some applications after upgrading. This typically occurs when upgrading from version 10.6 (Snow Leopard) or earlier to 10.7 (Lion) or later. The reason for this is support for Power PC apps was dropped. Snow Leopard, which exclusively runs on Intel Macs, still allowed the use of Power PC apps through Rosetta technology. Rosetta was removed in 10.7 Lion. Code designed for computers with Power PC processors cannot run on Intel processors without Rosetta.
Before upgrading, open your Applications folder. For any third party apps, right click (control + click) on the icon and click "Get Info." Next to "Kind:" it should say "Application (Power PC)" or "Application (Intel)." Applications marked as Universal or Intel will work, just not Power PC. Most software can still run if you upgrade to a newer version of the software. For instance, Microsoft Office 2004 or earlier will not work in Lion. Version 2008 or 2011 or later use Intel code and can run on Lion or Mountain Lion or later.