Not easy! But why do you want to do that anyway? Texture on drywall is applied to mask imperfections and compound humps. If you remove the texture, you will find out quickly just how out of flat it is.
To remove it, power sand it off. If painted, it will gum up the sandpaper. When you cut through it, you will probably damage the drywall face. In the end you will have to skim coat, and that is not easy.