Generally, the resistor is in the air duct, probably on the engine side of the firewall, passenger side. Look for a plastic plate with a black plastic plug with 3 or 4 wires going into it held on with two screws. Remove the screws and the resistor assembly will come out. It will look like a bunch of springs with the ends connected to the terminals that the plug attaches to.
The reason the resistors are in the duct is that they get hot and the air blowing through the duct keeps them cool.
Good luck