Hello,
If you have a valid RHEL license then you can register your server with RHN (if not already done at time of installation). After registering you can manage your server throught the RedHat Network at
rhn.redhat.com. Also when registered you can use yum, if configured correctly, to keep your server up to date.
Sorry to say but if you consider your server critical then I really don't understand why you haven't updated for almost 4 years. That's looking for trouble.
Kind regards,
Eric