Individual User Deactivation
Go to Users and select Manage All
Search for User and double click (or use the orange edit button) to open the User Edit screen.
From the Details Tab set the Users status from Active to Inactive Visible.
Inactive Visible will allow you to view the agent on reporting. If this information is no longer needed you can set the user to Inactive.
Update User to save changes
Multiple User Deactivation
Go to Users and select Manage All
Search for user and select check box to right of the User ID
Select Mass Edit on the top Middle of screen
Under Permissions, select from the User Status dropdown Inactive Visible
Update User to save changes