I'm not sure what you're asking. Do you want to reset the root password?
If that's what you want, you can append the "single" option to the kernel when you boot, and then use the "passwd" command ("passwd" is the correct way to change passwords); see this page
for more info.
Otherwise, if you can boot to a rescue disk or LiveCD like Knoppix or something, you can mount the drive and edit the /etc/shadow file on it and delete the root password hash.