The cottage cheese or popcorn texture can be removed with a scraper, such as a 10" wide joint finishing knife. Then some sanding will be required to smooth it out. Remember, textrues are used on ceilings in order to cut down on joint finishing. Where 3 or 4 coats of join finish is normally used, a texture will let you by with just 'tape, fill, sand' so, once you get the texture off the joints may need more finish to make a good job of the ceiling.
Its a lot of hard work and mess and I wish you the best.