Once a user account has been created, it cannot be deleted. This is because hearing records and activities are tied to that account.
However, the Manager can disable any user, if needed.
To disable a user, go to their user page and click on the orange Edit button in the upper left corner. Scroll to the middle, to the Section titled "Security" and uncheck the box marked "Enabled". Click on the orange "Save" button at the bottom of the page.
At this point, they will no longer have access to your account or