Valerie: first you'll need an asbestos test!
If they are clear of asbestos, work in small areas, misting with water and then scrape with wide scraper. Keep a shop vac handy and scrape with the vacuum head running near your work area will help keep the mess down a bit.
You'll need to patch and sand a bit when done. Good luck.
In my previous house they were sprayed Gunite- as in the concrete slurry that is sprayed to make built-in swimming pools.
Those do no knock down, they can’t be scraped - no matter how much one sprays them with anything. Bloody knuckles is all you get.
If one has gunite or asbestos, then they can be encapsulated with 1/8” drywall or completely filled in w/ drywall compound. The later is neck breaking work, but I chose not to buy drywall jacks.