If you're an administrator on your account, you can remove users from your organization. To remove a user, go to the "Users" page in the main Dashboard, search for the user -> Click the box next to the user's name -> Actions -- Remove User(s) from Org.

 A few notes:
-This doesn't delete the person's account–it only removes them from your organization. They can continue using MobileServe, but they can't report their time to your organization.
-Any past logs that are affiliated with the organization will continue to show up in reports run for that period.