RHEL 7 makes use of the subscription-manager and they have done away with the Classic registration in this version. You use the subscription manager to register, attach subscriptions based on support, and manage subscriptions. Once subscription-manager is set-up and subscriptions have been assigned, you can run YUM update just as before.
You can find out more by invoking
Code:
man subscription-manager
at the command line or feel free to contact Red Hat support if you are using their products. That is what you are paying for. If not, I suggest using CentOS instead.