It depends on which servo you are using. Most of the newer servos have both the pot and the motor installed on the PC board. If this is the case, you will have to cut the copper circuitry and install jumpers. If it's a pot with wires, there will be three wires going to it. In this case just reverse the two outside wires. You may also have to adjust the centering by loosening the screws holding the pot and readjust it. Not an easy job the first time.

I think I would wait for the servo reverser.