If you have admin privileges you can remove users for any user groups you manage. You can also delete a user completely so that their details are permanently erased from the system.
Admin status is flagged with this message at the top right of the screen when logged, which can be dismissed at any time:
To remove a user, go to My Account>User Group Management. If you manage more than one user group, select the user group you want to edit, and switch from app keys to users:
Mouse over the user you want to remove and use the trash icon on the right-hand side of the screen to remove/delete that user. You will need to confirm the action you want (either removal from user group without permanent deletion, or permanent deletion).