Remove the furniture from the room and cover the floor with plastic sheeting. Tape plastic sheeting over the doors, as well, to keep the dust in the room.
Stand on the ladder and spray a 4-by-4-foot area with the spray bottle until it is wet, but not dripping. Wait five or 10 minutes until the popcorn ceiling darkens slightly.
Scrape the ceiling with the putty knife to remove the popcorn texture. It will fall to the ground, where it can be removed later.
Spread a thin layer of joint compound over the ceiling with the putty knife. The joint compound will fill in holes and imperfections, readying the surface for stucco.
Sand the ceiling with sandpaper to smooth it. Cover the ceiling with a layer of stucco or spackle. There are several ways to accomplish this. You can spread it on in thin layers with a putty knife, creating swirls similar to the process of frosting a cake. Or, use a textured brush specifically for texturing walls and ceilings. Another option is to spray "orange peel" texture on the ceiling for a smooth, modern look.