If you are referring to a transmission Pan gasket, this can be replaced by first draining and removing the pan. The gasket that surrounds the pan is what should be replaced.
〉 Answered on Jul 10th, 2012 by Amanda J. Pierce, MBA "AJ", Certified Mechanic, Project Coordinator; Primavera Scheduler at VIGOR Alaska Industrial Shipyard & BizzM3ch Solutions
Unless you've done this kind of work before, it's best to leave it to a technician.
That being said, a service manual for your vehicle would show you how to do it and what tools are needed. You can probably purchase this on-line or through a dealership.
〉 Answered on Jul 10th, 2012 by Lori Johnson, Owner and Instructor at Ladies Start Your Engines