There are at least 2 kinds of texture being used on ceilings; one is compound applied with a stipple brush and looks like a patern of elephant tracks, the other is a spray that foams as it makes contact, we call that popcorn ceilings.
If yours is a popcorn ceiling you can scrape it off and finish up with a sanding pole. The elephant tracks are much harder; use a spray of water over 6-8 square feet at a time. The water will soften the stipple and it can be scrapped of with a little more effort, being careful not to dig into the sheetrock. Then you can sand it down a little to bring it to a more even surface, and last, skim coat it with more compound.
Either method is used to eliminate some of the joint finishing, so you may have to add another coat, touch sand and even use another coat to make it smooth and level, touch sanding again. It is a terrific mess either way with loads of dust. You will want to tape plastic over your door ways, cover your heat vents and return air vents, move the fruniture out, plastic tapped down to the floor, and wear a respirator and goggles.
I wish you the best success with this monstrous undertaking, be patient, use a bright light to shine over the surface to detect the imperfections so you can get them all.