I'm googling like a lost madman and can't find it :S
Well first edit /etc/mumble-server.ini
gksu gedit /etc/mumble-server.ini
sudo nano /etc/mumble-server.ini
If you want users to have to enter a generic password (same for everyone) to enter your server at all, set a password here, if you want anybody to be able to join leave it blank. Also just leave host blank.
Now to set your server name, look for the section below, delete the '#' in front of registerName= , put whatever you want your servername to be after registername=
# Specific IP or hostname to bind to.
# If this is left blank (default), murmur will bind to all available addresses.
# Password to join server
Now restart mumble-server for the setting to take affect
# To enable public server registration, the serverpassword must be blank, and
# this must all be filled out.
# The password here is used to create a registry for the server name; subsequent
# updates will need the same password. Don't lose your password.
# The URL is your own website, and only set the registerHostname for static IP
Log into your server with a client, for the ip just use 127.0.0.1 use the user name you want, once logged in click your username, click self, click register. Log out.
sudo service mumble-server restart
Log in as SuperUser, enter the superuser's password. Once logged in Right click your root channel, click edit, click the groups tab, edit the admin group and add your user.
This site is for windows put should give you a visual idea of what I'm talking about.