All Follow Up Boss users can delete their user account at any time. Please see the process below depending on your user role:
As account owner you can cancel your entire Follow Up Boss account, please see this article for details - Cancel Your Account.
Admin, Agent or Lender
Non-account owner users can delete their user account by going into My Settings from the user menu in the top right corner:
and then clicking "Delete my user account" link at the bottom of the screen: