Nothing to it. If you have a plastic catch pan, replace it with a metal one (some home inspectors ( if you're selling) will complain about plastic). Replace the pressure release valve, make sure when you install the new one you have in and out oriented correctly. Make sure your exhaust stack is taped back up well with foil tape at the joints. Compound or use gas tape on the joints.
Good luck!
Charlie
^^^^^This
I think the hardest part is where yours is located and to add little to what Charlie said, make sure and soap water test your connections when you're done. A couple hrs and you got this