Username - changed admin setting, can't log in!

Having started to check out all the facilities on the trial version installed via xampp/localhost on my laptop, I innocently decided to change the admin setting ‘use e-mail as username’, then logged off and now I can’t log in as ‘admin’ anymore!!

Is there any way i can get round this, or will I need to do a re-install?

I should have read the other posts first! Back in control again - hurrah!