If you are certain it is not a support wall, and all power is de-energized; I prefer the direct appoach to taking down a wall. My tools of choice include prybars, crow bars and mallets. Brute force is highly recommended so that by the time you get to the building phase your softer artistic side is more freely expressed. LOL
Artex is a brand name for texture finishes. It shouldn't actually change your normal demolition methods.
If your post is refering to changing the texture to knock-down, or just simply removing the texture, then a gentler approach may be warranted. In that case you need to either remove the texture or the drywall it is on. I never tried to remove this material. Artex is uaually very thick and tends to adhere pretty tenaciously so you might be better off going with new wallboard. If all else fails see their website which posts technical articles on maintentance at