Jack the car up on jack stands or car ramps to permit easy access to the muffler and exhaust pipe. Disconnect the negative terminal on the battery before starting muffler removal.
Apply penetration oil to muffler clamp nut and all fittings, as chances are good these fittings are coated with some rust due to the car being driven through rain puddles and snow.
Cut the pipes leading to and from the muffler with a hacksaw if the muffler is welded or if the nuts are not adequately loosened for removal after being sprayed with penetration oil.
Use an impact wrench to remove the nuts from the muffler hanger. Let muffler drop down to loosen it from the rear mounts.
Pry the muffler from the rubber straps holding it in place with a pry bar and remove. Inspect rubber straps to make sure they are not worn; if so, replace them before installing the new muffler.