Old texture can get, well, old, and you may be hankering for a change, especially if it's the type of popcorn texture popular in the '60s and long since out of style. If the texture predates 1980, however, it may contain asbestos, and if so, the law prohibits you from removing it yourself. To find out whether you need to hire a professional, collect a small amount of the texture in a plastic bag and have it tested; your local building department can help you find a lab. If you're in the clear, prepare for a messy day of scraping.
Remove all furniture from the room, open the windows and cover woodwork and built-in cabinets with plastic sheeting. Spread plastic sheeting on the floor, overlapping the sheets and taping them together to prevent material from falling between them. Tape the top of the wall around the perimeter of the ceiling with painter's tape to prevent damage to the wall.
Sand the ceiling lightly with a pole sander and 120-grit sandpaper. The purpose of sanding is to remove paint and expose some of the texture material.
Mix 2 to 3 tablespoons of dishwashing detergent per gallon of water in a garden sprayer. Spray a section of the ceiling thoroughly and let the soap/water solution soak in for about 10 minutes.
Climb on a stepladder and scrape the section of the ceiling that you sprayed with a 6-inch drywall blade. It's a good idea to round the corners of the blade with a grinder so that they don't dig into the drywall. Don't overscrape. If some of the texture won't come off, leave it for now.
Rewet the section of the ceiling you're working on, but use less water than before to avoid damaging the drywall tape. Wait 10 minutes, then scrape again to remove residue. Scrape lightly over the drywall tape to avoid lifting it with the blade.
Let the ceiling dry after you've scraped all of it and sand off any residue with the pole sander and 120-grit sandpaper.
Repair any lifting or damaged drywall tape by coating it with joint compound and scraping the compound flat. Fill nail or screw holes and scrape them in the same way.
Give the ceiling a final sanding with 120-grit sandpaper after you've repaired all the drywall joints.