You should try to keep you Chromebook up to date. The newest version of ChromeOS lets you know that it needs an update.
The easiest way to do that is to make sure you log off or power off the Chromebook when your are done using the Chromebook(push the power button or click in the tray and click on the power icon.
You can also force an update. Watch the video to learn how to keep your Chromebook up to date.