Here are the first things I would try to do if you have lag:
If you don't know how to do these things, then use the video tutorials below.
How do I delete my browsing history on Chrome?
*** Please note you will NOT be able to delete the browsing history, however you can remove all other items (although I would not advise deleting user names and passwords).
DeletingBrowsingHistory.webm
How do I update Chrome?
How do I update the Chromebook Operating System?
How do I remove additional Extensions from Chrome?