The stock should be attached with a normal bolt (ether hex-head or slot-head) through the top of the pistol-grip at an angle into the back of the receiver. Sin that off (you may need a longer one to mount the new stock), and the rear part will be free. To take the forearm off, you'll have to strip the shotgun down and take of the forearm with the action bars attached. There's a little threaded collar inside the front of the forearm that holds the wood one, and you can spinn that collar out with a pair of needle-nose held at the correct spacing (there IS a wrench available, but unless you're doing this on a regular basis, you don't really need the wrench.) HTH.