The best way to upgrade you car would be to fix the Audi TT side skirts. If you want to make your car to be looked closer to ground, you can attach the Audi TT side skirts to the sides of your car. These are essentially the strips of carbon fiber, plastic or fiberglass that normally tends to suit with the default body stripes of your Audi TT. Their attachment and installation is quite simple and it enables to use it together with rear or front bumpers.