How do I replace the ring gear and pin...

You can change the ratio back to 4.10. However, if you do not already have the specialty tools required to do the job, you will likely be better off finding a shop that will change the gears for you. A mistake as simple as incorrect backlash will result in destroyed ring & pinion gears.

Your cheaper options will be :
1. Find a matching rear-end with 4.10 gears and swap it in.
2. Purchase the ring and pinion, master install kit, and find a friend that has installed gears before to help you out.
3. Find a 4x4, Hotrod or auto shop that is will swap the gears for you. If the axle is in the car, it's usually more expensive than if you carried the axle in for them to work on.
4. Purchase R&P, Master install kit, all the required tools. Then hit the books to find the proper procedure and measurements for that axle.

Good Luck.