Change the password? Or do you mean prevent them from "su"ing to root...
I think on RedHat (unlike FreeBSD), the best you can do is to set: "PermitRootLogin yes" to "no" in your /etc/ssh/sshd_config, so that you can't ssh to root, but you have to su from a user. But this still won't prevent a user from su-ing.
The user should not be able to open the /root directory or see files that are not marked readable for world or for his username.
If your user can do that, then you've got a serious permissions problem.
In any event, allowing anyone SSH is definitely a security risk; we don't allow it except by special need, and then we require a written agreement of liability.