If you're planning to buy a replacement from a store or online, you just need to tell them the year/make/model of your vehicle and they will send you the correct replacement muffler. No need for guesswork. The parts are matched on computers so you shouldn't get a wrong part. You can ask the person you're buying the muffler from whether it's a simple bolt on part or if you'll need any welding done.
If welding is required, you'll probably need to bring it to a shop to have them raise your vehicle on the industrial lifts and unweld your existing muffler to get it off. Then put on the new muffler and weld that in place.
