How to Update Your Chromebook
Sign in to the chromebook
Open chrome
Click on the three dots in the upper right corner of chrome
Hover over Help (towards bottom of menu)
Select About Chrome OS
If it doesn't start checking for updates automatically, there will be a button you can click to check for updates.
It will go through the process of updating & then have you restart the chromebook.
Repeat the process until it says the chrome OS is up to date.