Textured finishes are usually done with Joint Compound, which is water soluable. The question is; was it ever painted? If so, you may not be able to remove it. I have removed texture by spraying it with water using a "compression sprayer" (one of those sprayers you use in your garden that you pump by hand). This can lead to some problems. I'm assuming that the texture is over drywall and that it was done by a Professional. In most cases, the drywall wasn't primed before the texture was applied. Spraying with water will soften the texture, and also the drywall and the taped joints. This means that you'll need to repair alot of the drywall and the taped joints.
The process is messy. Remove everything from the room and cover the floor with heavy dropcloths, then cover the dropcloths with 3 or 4 mil plastic, taping the joints of the plastic with duct tape. Then spray an area of the texture with water and allow it to set for a few minutes. Spray only an area that you can keep wet and get stripped before it soaks into the drywall. Spray a second time and allow to stet for just a couple of minutes then get up on a ladder and scrape the texture off with a 6" taping knife. I have held a mudpan under the knife to catch as much of the texture as possible, which cuts back on the mess. When you've removed all the texture, go back and wash with clean water and a "Clamshell" sponge.
This is the kind of project that, once you have started, your committed to it. Nothing looks as bad as partially removed texture and patching in texture never looks a good as the origional.