Your Chromebook should automatically check for and download updates when connected to WiFi, however you can check yourself. This will sometimes solve issues your Chromebook may be having.
Turn on your Chromebook.
Make sure your Chromebook is connected to WiFi.
Login to your Chromebook
At the bottom right, select the time
Select Settings (top of box that pops up)
At the bottom of the left panel, select About Chrome OS
Under "Google Chrome OS," you'll find which version of the Chrome operating system your Chromebook uses
Select Check for updates
If your Chromebook finds a software update, it will start to download automatically
Note: If your Chromebook uses your phone's internet connection or its own mobile data, you'll get an alert about how much mobile data it needs to update. You can then stop or continue with the update.