For this achievement, you just need to win a race with a tuned car.
To tune your car, go to the garage, select the car you want to use, and select the tune option (in between visual upgrades and performance upgrades).
All you need to do is adjust one of the sliders to the right or to the left, but I would suggest tinkering with it a bit to find which tuning setup works best for the way you drive.
After you tune your car, just go win any race and the achievement is yours.