EDIT: If you already have completed Upgrade Heroes and have all the stars, this achievement and the other Upgrade Heroes achievements should unlock when you load the game. Thanks LeGagnan!
So kinda like some of the other Forza Horizon 4 businesses/story missions, you will need to get 3 stars on 10 missions.
Before you start Upgrade Heroes, make sure you have 100,000 CR as you'll need it to purchase the business.
You'll get a daily CR payout after purchasing.
The majority of missions will start with you driving to a point, getting the car and bringing the car back to the spot to "upgrade" it without going over the damage limit. Those parts do not count towards stars. Just don't damage the car too much when bringing the car to wherever as you will have to redo that part of the mission.
After the car has been upgraded, go crazy with shortcuts and offroading as it'll be needed for a lot of the missions (except for the final mission).The Challenges
1. The Datsun - Finish in 1min 28sec
2. The Audi - Finish in 2min 15sec
3. The Camino - Finish in 1min and stay above 100mph or 160.93km/h.
4. The Mazda - Get 80,000 drift points
5. The Chevrolet - Reach 185 mph or 295km/h at the Speed Trap
6. The Land Rover - Finish in 1min 40sec
7. The Peugeot - Get over 180,000 skill points.
8. The Ford - Finish in 2min 10sec
9. The Bentley - Finish in 2min 20sec
10. The Koenigsegg - Finish in 3min 20sec and don't go over the damage limit.
If you got all 3 stars on all 10 missions, you should unlock this as well as:
If you need some visuals, I used this video (credit to MotoGamesTV on YouTube):
Let me know if there are any improvements to the solution that need to be made and I can edit. :)