How get change root Password

You can log in with single-user mode and create a new root password.

If you are currently set up to log in to X rather than a
console, you will need to press [Ctrl]-[X] when prompted. When you
see the boot: prompt, type linux single to enter single-user mode.
Some of the filesystems will be mounted, and you will find a bash#
prompt when you've entered single-user mode (note that this prompt
will look somewhat different than the prompt you're accustomed to).

Now, you can change root's password by typing

bash# passwd root