You have to basically gut the entire receiver, which is all but impossible without the right tools, and if you're asking how to do it, you don't own the right tools. The firing pin block which houses the firing pins is one of the last things to come out of the receiver.
I would suggest you have an annual done at the same time if your gun is close to needing one, it will be just as disassembled to change the pin as it would be to do an annual.
If you can't find anyone local send it up to me. I'm in NW Oklahoma and UPS from Dallas is one day. I've got a large stock of parts and can turn it in a day. Don at Krieghoff Int has sent a few to me that we're in a hurry. Larry
I have K guns that I do not shoot a lot and have never changed the springs since I only shoot about 2000 rounds a year. The annual IMHO is like the add on service contract on your TV, it's a money maker for the company. When it's broke fix it. Bulge.
I have changed firing pins in both my K-80 and my Rem 32. With the 32, I went to two piece firing pins. I used one piece firing pins on the K-80. ( I have not seen Two piece firing oins for the K-80) K-80 manuals seem hard to find, but you can find a Rem 32 manusl, and changing the firing pins is the same.