The plastic part that surrounds the instrument cluster must be removed first. The steering column usually needs to be loosened also to remove the plastic piece. Then the trim piece that covers the heater controls needs to be removed. Now you have access to the screws that hold the heater lever assembly in place.
I don't recall if the lever assembly comes out enough to remove the cables. It may be necessary to undo the cables at the heater box to get the lever assembly out.
Best of luck,
Loren