Replacing the tank is easy, just screw the old one off and screw the new one on. Best to turn the water off first, and you do have to set the pressure to match the PRV. I'm not sure the cause of you problem is tank failure, but the pressure needs to be checked and set if necessary. You do this with a hand pump like used for bicycles and an ordinary tire pressure gauge. You can check the tank's condition by removing it and seeing if the tank is full of water. Should I point out that if the tank has failed is is full of water, it will be fairly heavy? You should also have a pressure gauge with adapters that can be screwed onto a water faucet to check the PRV pressure. These are available at any hardware store for under $15. I actually permanently plumbed one into my supply line so I can check the pressure at anytime with just a glance.