Slide any furniture out of the way, if it's blocking the wall. Place drop cloths on the floor directly in front of the wall. Put on goggles to protect your eyes, a dust mask to protect your lungs and possibly a cap to protect your hair from the dust.
Install an 80-grit or 100-grit sandpaper belt on a belt sander. Switch on the sander's power.
Hold the belt sander with both hands and ease it onto the wall. Do not put any pressure on the sander. Instead, guide it and keep it moving across the wall surface to sand the texture paint off. Don't hold the sander in one spot.
Sand off the Homax texture paint, making sure you don't sand down into the drywall underneath the paint.