Glenn Golden
Ah, now it is time to hit the database directly. Dig up the sakai_user.sql DDL, find the line that inserts the "admin" record, go to your database, remove the existing "admin" record, and run the insert. That will give you "admin".
Then go change it. You will also have to reset the name you assigned to the admin user, email address, etc.
It is pretty standard practice to add some normal users to the authzGroup (realm) "/site/!admin", i.e. add some users to the admin site ("!admin"). This makes these users admin users, with the same powers as the one called "admin". That way you can do things as individuals (instead of the system administrator), and also it gives you a few users who can set anyone's passwords (including "admin").
Glenn Golden
Any user who is a member of the site "!admin" (i.e. in the authzGroup "/site/!admin") with the "site.upd" role is considered an "admin" user (if the application doing the consideration goes through the Sakai SecurityService), and will be granted all the privileges as the actual user called "admin".
This is, I believe, the more standard practice than actually using the "admin" account.