How do you replace the blower for the front seats. on 2007 Cadillac DTS

The seat heaters do not come on when it is cold like they are suppose when you start the car. I was told that both blower motors were blown. How can i test this to be sure? Can I change them on my own or do I really have to go to a dealer to have this done.

Asked by for the 2007 Cadillac DTS