Turn the power off to the room by flipping the switch in the breaker box.
Use a screwdriver to remove the light fixtures from the ceiling. Untwist the wires and set the fixtures aside. Ball up some plastic, such as a shopping bag, and push it into the light fixture hole to protect the wires from moisture.
Place plastic sheets down over the floor and tape them to the wall edges with painter's tape.
Tape more plastic sheets to the walls and cover them all the way to the floor. Tape the wall sheets to the floor sheets to completely seal all surfaces except the ceiling.
Fill a spray bottle or garden mister with water. Spray the ceiling in a small 3-foot section to moisten the surface. You want the ceiling damp, but not soggy.
Scrape the ceiling with a small trowel or taping knife. Use a blade with rounded corners so that you do not gouge the drywall. Continue scraping until the 3-foot section is virtually free of texture. Repeat with other 3-foot sections until the ceiling is clean.
Cover the floor with a second layer of plastic and go over the entire ceiling again to remove any remaining texture.