I recently had to replace mine (the black one actually broke at the blade). I used Valterra replacements as they hwve a nice quality construction. The siae of each valve you need is on the valve usually on the flat valve area. Dump and get the tank as empty as possible. Have some paper towel or shop rags. Wear gloves. Remove the four bolts (ratching wrenches and box wrench. Once you remove the bolts you can pull the valve out from the pipes. It will be quite a tight fit but you can flex the pipes. There are two rubber seals one on each side. Remove. The reverse installs it. An extra pair of hands may help but i was able to do it myself. Like i say the pipes are quite flexible. Put the new seals on the new valve and get it seated. Then tighten the new bolts. Dont over tighten...it is just all plastic.
Plenty of videos if you ask google. But it really is just four bolts and pulling the pipes apart enough go slip it out and a new one in. I went ahead and did both. Mine required dremeling away the flat part so i could grab the valve with a pair of pliers to dump. Then it was the same as yours. About 30 mins first valve....15 second.