If you login as root at the cmd line and do
yum update <something>
replace <something> with eg httpd, it will attempt to contact RHN (Redhat Network).
If it says 'not registered', then you need to find the subscription id the system came with IF(!) it was originally bought and not a free 30 day Trial.
You can also just phone RH support and give them your company name for instance and have them search the registration DB.
If it turns out you don't have a paid subscription, then you need to pay and then (as root)
giving the subscription num supplied by RH.
This gives you a) updates, b) support), c) access to RH Knowledge-base etc
If you don't want to pay, then you can move over to Centos, but that only includes updates; no support/knowledge-base.
You'd have to use google/LQ instead.