All you needed was a password why would you change the account type? I doubt someone could really be that dumb. If you didn't know what you were doing, Microsoft provides pleanty of help with the "learn about" section in User Accounts. Which you should have read before making changes.
Most people with little computer knowledge are hesitant to make changes like that without knowing what they're doing.
If you look at the menu when editing accounts Create and Change Password come before Change My Account Type. Also even if you did manage to over look it, there always has to be at least one administrator.
Notice, limited is greyed out and check out what it says on the top. Since you "own" the box (assuming your story is true, there'd be another admin) you should know all the admins and have them fix your problem. Otherwise you're just basically asking how to privilage esculate.