Your car has 3 cats. Two are right at the exhaust manifolds on each cylinder bank. These are monitored for function and will throw codes (P0420 / P0430) if removed or gutted. The third cat in the exhaust pipe is not monitored and could be removed. Removing this cat will not increase performance or MPG in any way unless it is plugged / melted. Removing it will just make the exhaust somewhat louder.
If you want to remove the third cat, measure the diameter of the pipe, length of the pipe needed, and head to the parts store and buy a piece of pipe longer than your length measurement (so you can cut it to the correct length), some clamps and have at it.