As root, you have to use the "passwd" command. I believe once you're root, you just need to type passwd and hit enter, to be able to change root.
Here's a link to the man passwd page: http://linux.die.net/man/1/passwd
but i forget to say that i dont have root password.
The passwords are usually in the /etc/shadow file (they are not simple text)
If you happen to know any user password copy it from that file to the root line. For this of course you'll need to chroot to the partition (whether it'd be from a livecd or inserting the hard disk into another computer)
Comments
Here's a link to the man passwd page:
http://linux.die.net/man/1/passwd
/P
The passwords are usually in the /etc/shadow file (they are not simple text)
If you happen to know any user password copy it from that file to the root line. For this of course you'll need to chroot to the partition (whether it'd be from a livecd or inserting the hard disk into another computer)
Regards