Unplug the Genie garage door opener. Remove the lens cover that covers the light bulbs. Note the six screws labeled one through six. Remove the white wire with the U-shaped connector from screw one. Leave the other wire on screw one. Remove the black wire from screw two and the red wire from screw three. There shouldn't be any other wires on screws two and three.
Remove the screws that hold the GR 390-12 receiver box to the garage framing. Mount the new receiver box in the same spot.
Slide the white U-shaped wire connector around screw one. Slide the black wire connector around screw two and the red wire connector around screw three. Tighten all three screws to secure the wires.
Open the cover of the receiver box by squeezing the two long sides of the box casing. Slide the small 12 switches either up or down with the screwdriver so they match the 12 switches found inside the remote control. Plug your garage door opener back in.