Lay drop cloths on the floors and secure them to the walls. Remove anything from the room that you can pick up and move out. Open windows and doors for ventilation.
Do everything in 4-foot sections. Fill a spray bottle or use an electric sprayer with a water supply. Spray a 4-foot section. Let the water absorb into the ceiling for 15 minutes.
Scrape the water-soaked texture off the ceiling, using the floor scraper. Remove only remove the texture material. Stop if you hit the drywall.
Continue to scrape in 4-foot sections until all the texture is gone and the ceiling feels smooth. For stubborn areas, use more water and let it sit for 15 more minutes. If the texture is thick, you may have to repeat the process a few times to get it off.
Fill in any areas that seem uneven or have holes in the drywall, using drywall mud and a drywall trowel. Do not be heavy-handed, as a light coat should suffice.
Allow the ceiling to dry. Apply a coat of primer and allow it to dry before painting.