If you can get into phpmyadmin for your WordPress database, you can click on the wp_users table, click the Browse tab, and then find your user.
Click the little pencil icon to edit that user
Change the username to whatever you want, and change the password to this:
that is MD5 for 1234 (thus changing your password to 1234)
Click the go button to save...that should do it. Your login name will be whatever you changed it to, and your password will be 1234
Of course, immediatley change your password to something complex after you are logged in.