as far as I know, the admin account is only visible in the welcome screen when there are no other user accounts(and when you're in safe mode) if there are other accounts, the admin should be hidden.
and if its hidden, it shouldn't be bothering you...
I don't really think you can delete it, and besides, even if you could, that would not be a smart thing to do.
The admin account's main purpose is to be a "back door". should something happen to the other user accounts preventing log-in (or some other drastic issue) theoretically, you can log into the admin account and correct the problem.