ok so the first enemy, the pink car has 1 screw on the second level, you should be able to catch this screw, if you upgrade your car with coins till lvl 4-5 in speed and acc.
and with this screw you can upgrade your car further and it gets to level 6-10 and you can unlock the next enemy.
always repair your car when you come back from a race, not just when the sprites changes, you wont need screws then.
I dont work on the project anymore, because i do other projects, check out my other game and try to reach the highscore, its more polished and playable :D