How do you increase the speed on a radio controlled car?

Answer 1

RC car speeds are mainly controlled by the gearing and the motor. There are different motors( # of windings, etc.) that control if it makes it's best power for light high speed car or heavy 4x4 RC trucks.

Answer 2

If it's a preassembled one you might not be able to, but the ones that come more as kits will usually let you replace the crystals that controls the frequency of both the transmitter and the receiver.