Start a new Tournament ang go through the track, after the match is over go to the Vehicle Upgrades Screen and buy any upgrade, the cheapest ones are the Traction upgrades for 250 credits at first, you'll have more than enough.
You can access this screen anytime after you select a new track on your campaign and before you start the track.
If you want to get it before doing a track, you start the tournament with 1,000 credits, more than enough, I recommend racing a track first to get some credits and better upgrades.