These instructions apply to Mac OS X 10.6 or higher.
First, launch your favorite browser (Chrome, Firefox, Safari, etc). Enter the following URL:
This should show you what you have installed as your current version of Silverlight.
If you already have the latest version, you'll see it without a link, in which case you're done. STOP here.
If it's old, or doesn't exist, you'll see the latest version as a link to where you can get it.
Click that link and download the Silverlight.dmg file. Then, quit from ALL browsers you may have active, including this browser. .
From "Finder", navigate to your hard disk (in column mode), and then follow the path:
If you have either of the following, Trash them:
1) Silverlight.plugin
2) WPFe.plugin
You may be asked for your Password to complete them. If you had one or both of them, then check this path:
And Trash the corresponding .pkg, if you have them. At this point, your old versions are "Unistalled".
Now, from "Finder", navigate to YOUR download folder. It may be Downloads or Desktop, or whatever you told your browser to use for downloads. Double-click on the Silverlight.dmg to open it. Inside you'll see a silverlight.pkg, which you double-click to launch.
Follow the instructions. Your Destination will be either a disk choice, or "Install for all users". You may be asked to Authenticate again.
Once installed, relaunch your browser and check if it is known to your Add-ons -> Plugins.
It should be called: Silverlight Plug-In with the version number you downloaded. If it's your old version, you may have skipped a step, or just try once again.