The hopup could be damaged?
Well to my recollection (I dont have the gun in front of me so I am just doing it by memory):
There are two notches in the center of the frame push down both at the same time and the upper slide should slide forward and away from the frame. (Comes off the way the bb shoots out)
The Recoil spring comes off next. There should be a flat part of the recoil mechanism that hits the outer barrel. Push on that piece it should retract pull it away and it should come off.
Then just slide the outer barrel out and the inner barrel and hopup should come out too.
Take out the inner barrel and hopup unit it should come out together.
Check the hopup rubber on the inside and see if is torn or damaged.
What types of bbs were you using?