How do you replace all the tires on a 5th wheel?

Most tire shops can accommodate trailers. Like mentioned, call ahead of time and let them know exactly what you have and the weight. I stayed with mine when I had last set replaced because I wanted to do the jacking. They had no problem with that. Do your research on tires. Don't settle for the Chinese brand that they tell you they carry. Go with what is recommended on this forum.
Good luck.