You need a fly wheel lock tool, available from most VW parts suppliers.
You will also need a breaker bar to get the leverage you need, and a torque wrench that goes up to at least 260 newton meters to do it back up.
Also mark the position of the fly wheel to the case with number one piston at the top of its stroke. The reason for this is the fly wheel is balanced to the crank, and there are only 4 dowel pins holding it in place, so its possible to refit the fly wheel 90, 180, and 270 degrees out of position. Try not to turn the crank once its off each piston has two top dead centers per cycle of the engine, and you might not get the right one.
Lastly get some thread lock for the gland nut, and its really important that you get the nut torqued up to the correct torque.