You have to use the superadmin login page and login information as the superadmin is now the only person who can still grant you serveradmin rights.
Please note that you have to define a new password when changing the serveradmin status of a user through the web administration interface. This is one of the remaining bugs in TeamSpeak 2.
You don't have to set a new password when using the
TCP query interface which is documented in the
updated server manual.