From the Administration tab, click on the Users
tile.
Double-click the user account you want to disable.
The User Properties window will
be displayed.
Select the Account Disabled check box.
Click OK to save the user
configuration.
For better organization of
users, try using the 'Group By Box' found under view. Once enabled,
click and drag the 'Active' column to the 'Group By Box' area.
This will split the two groups into Active and Inactive users
for simpler management.