Get better car that has upgraded tech available. You will see it.
What he said, although I think it's stupid you can't get all the upgrades on all the cars.
sure you can. once you start getting cars with the ability to take higher upgrades, they will all accept them.
Are you sure? After I finished unlocking all the cop cars, and bought all the upgrades on the cars I actually use I decided to go back and just buy them all for completion sake and on the lower ranking cars I never got the option to buy anything past the same 4 level 1 techs.