Sorry, I was being a dick. If you want a lot of horsepower you will either have to swap out the motor or turbo it. I dont know if there are any turbo kits made for your car yet. What you do to your car really depends on your budget and your end goal for the car. If you want us to help you, we need more details.

P.S. A full cat-back exhaust will not give you much horsepower, maybe 5 max. For the price, I dont think it is worth it.