If you no longer need a named user, you can unregister the user to free up the license. The user will no longer have a reserved license, and the license can then be re-allocated to another user.
Unregistering a named user removes that user's reserved license, but it will not necessarily prevent the user from logging in to the repository. The user could still be able to sign in using a named device or WebLink via a public portal license. If you want to make sure the user can no longer access the repository at all, you will need to either remove them from the repository, or change their authentication status to Denied.
Important: Be aware that Active Directory Group Synchronization rules can automatically re-add named users that you manually remove.
The 
button saves a comma-separated (CSV) file of all registered user accounts in the Directory Server site.