Open the Navigation Permissions tab on the Role screen.
Click on the empty line to create a new Navigation Permission.
Select a Navigational Menu item that you wish to grant/revoke. In this case the Permission Policy is set to 'Allow all by default' and so all the navigational items currently have Navigation Permissions granted. In this example we will then be revoking Navigation Permissions.
Selecting 'Maintenance' and setting the 'Navigate' permission to 'Deny' will revoke navigational access to this menu item and all menu items that fall beneath it within the Navigational Menu.