You should open up your usermanual and turn to page 59. It will tell you how to do it.
#1. Remove barrel
#2. Remove slide
#3. Remove Trigger
#4. Remove screws inside the recoil pad. Two really small holes.
#5. Remove Hex nut with 1/2 socket(deep or extenstion will work).
#6. Remove the stock by turning it counter-clock wise.
*** now just reverse the steps with the new stock.***