How do you remove air chamber of Crosman 120 air rifle?

Crosman has diagrams for most of their air rifles. I checked and of course the don't have one for the 120, BUT they do have one for the 140 which I believe is very similar Go towww.crosman.com and click on "Down load a Manual" you will find help there. BTW the take down screw is on the bottom of the stock. OR you can go on-line and find a repair station. Check "Airgun repair" in the web.