To clear Cookies and delete the temporary files in the Chrome Browser, click on the More button (three dots stacked) in the upper right corner of your browser, click on "More tools", and then click on "Clear browsing data..."
In the window that pops up, click on the "Advanced" tab and only check "Cookies and other site data" and "Cached images and files" only. For the Time range select "All time".
Then Click the "Clear Data" button. It may take a few minutes to clear that information.
Note that student's are no longer able to delete their own History in Chromebooks owned by the school.