Ok you need to log in as root user. Once logged in you need to left click on the desktop or ydl start icon and scroll through main menu application/accessories/system tools/system config Look for users and groups. Here you will be able to add new users and delete unwanted ones.
I hope you remember your root password. It is much needed like a vital organ. If not my only other suggestion would be to reinstall and be very careful at root password prompt when asked during reinstall.