Step 1 - Connect to your Mumble server as an Admin.
To connect as an admin you can log in to your server as "SuperUser" or an account with Admin Privileges.
Related Tutorials: Connecting as "SuperUser", Creating a Server Administrator.
Step 2 - Accessing the Regisered user admin in Mumble
In the upper left menu of Mumble click on "Server" then "Registered Users".
Step 3 - Removing the registerd user.
Click to highlight the name of the user you would like to remove.
Once highlighted, Click on the "Remove" button.
If you are finished removing users then click "OK".