Gently warm the stone, this is to help loosen the residue buildup that may have occurred during usage. After that, firmly and as flat as possible, turn the pipe or slide over and tap on a soft surface. 1-2 firm but soft taps, should remove the stone from the pipe or slide. DO NOT use tweezers or any other tool, unless you plan to destroy and replace with nice one.
If the stone is being stubborn, try soaking the entire pipe in ISO for a hour or so, to help loosen any residue. Drain and try tapping the stone out. OBVIOUSLY do not use any flame using this method. Make sure to fully let everything dry out completely before using. Once the stone is removed and dry, torch it until glowing orange and let cool down 15 min before using again.
Usually the initial method is the preferred method, but ISO will work and be ok, but requires more attention by the user.