Username is the e-mail you used when registered an account. When you registered you recieved mail with confirmation that the registration was successful. All actions done inside our system uses your unique e-mail adress and we can´t change it. You need to contact us for further help or create a new account.
You need to contact he administrators if you still can't figure out which username you have by e-mailing email@example.com.
Note: we can't change your username or retrieve your old password.