Caveat: If you never drive on a track, the aero "upgrades" you're looking at don't actually do anything, or your car is too slow to ever generate downforce, just walk away.

If you're looking to shave off a few tenths from your lap time and you don't want to practice, a great way to do so is to upgrade the aerodynamics of your car. You can lower drag (which also helps fuel economy) or generate more downforce for better handling. Just don't throw a replica of the McLaren MP4-12C GT3's wing on an old Honda Civic, you'll just look like an asshat.