How do you change a new administrator account back to the old one on Windows?

Well I though you could make 2 administrator accounts but I guess you couldn't. The old one disappeared when I created the new one. How do you switch it back to the one it previously was?Please Help I am going to be in so much trouble if I can't change it back!
How do you change a new administrator account back to the old one on Windows?
You obviously can't have 2 accounts with the same name, but you can have multiple admin accounts.
Reply:Have it by another name. You can't have 2 or more identical accounts.