I found this in Kevin Southworth's blog and I think it's worth mentioning since it may save your life in case you have forgotten your superuser's password. Using SQL, you can promote a regular DNN user to a superuser like this:
DECLARE @username varchar(50)
SET @username = 'theUsernameToPromote'
IsSuperUser = 1
username = @username
WHERE username = @username)
Simply replace 'theUsernameToPromote' with the user name you need.