when removing the popcorn spray the ceiling,mist it with water.we used a pump up sprayer wet a small area let set for a little bit then scraped it off.it's easier to clean when wet. Besure and use a good respirator don't soak it just lightly dampen makes thing work better.also cover anything you don't want it on.
House is empty now, we're doing this before removing the old carpet, then clean the floors, then install new carpet. We're also painting pretty much the entire house too.