How to change user account actual file name

Yes, I now understand the explanation and appreciate it very much. Thanks to all who responded.

But what I still don't understand is why the creation of a new user account, say Bill, then logging in as that user, and deleting all that user's newly created folders, and then copying over another user's complete folders/files listed under their user account (e.g., C:\users\John\*.*) to C:\users\Bill\ didn't have the effect of transferring John's account over to Bill's? Instead, after the copying was completed, every time I tried to login to Bill's account, the system created a temporary profile and the account did not have John's folders and files? I must have done something wrong because if I'm understanding correctly, this procedure should work to move John's account over to Bill's account folder, shouldn't it?

An excellent post from Iseeuu, worth to read if you want to change the name of the user: Directory Username Problem

+1