To edit a user, right-click on it in the list and choose Edit User. The Add/Edit dialog will appear:

 

 

Users can be enabled or disabled by checking the Enable user box. When a user is disabled, he/she will not be able to log in or perform tasks.

 

There is also a pre-existing Guest account which can be disabled but cannot be deleted. This is the default account used for any client that does not authenticate itself.