Do not just Sign Out or close the Chromebook lid; actually Shut Down. Once you sign out, there will be a Shut Down button in the lower-left corner and a shut down button within the settings pop-up window in the lower-right.
Steps
Expand the Chrome Menu (3 vertical dots in the upper-right corner).
Click Delete browsing data.
In the pop-up window, select the Basic tab.
In the drop-down menu, set the Time Range to All time.
Make sure the boxes are checked next to "Browsing history", Cookies and other site data", and "Cached images and files."
Click Delete data.
Repeat as needed. (We recommend making this a weekly habit.)
View the Step-by-Step Guide >>>
After you sign out, click the tiny down-arrow next to your name on the login screen. Select "Remove user" and click "Remove user" again.
Sometimes it helps to disconnect/forget the network, then reconnect. You can do so within your Settings on the Chromebook.
Your Chromebook operating system (Chrome OS) is supposed to update automatically, but sometimes it gets behind. If it gets more than two versions behind, it stops auto-updating. Follow these steps to update your Chrome OS so you are running smoothly.