Remove the barrel, then slide a finger up into the bottom of the receiver through the bottom magazine loading port and push out on the right, then left or left, then right slider retainer flat spring(s), one on either side, while gently pulling forward on the forend slide. The dual slide bars are released and the whole works simply slides forward on the magazine tube. Put it back the same way; really, it couldn't be easier. If you wish to remove the trigger/hammer assembly, first, punch out the two pins and it pulls straight down and out. You gain a little more working room and can see what your doing, but it's not necessary. The gun should be right side up.
It takes longer to say, than do......hope this helps .....mike
slide the pump action over the shell tube and let it sit just before that action. set the greyish metallic piece on the two long flat bars, might have to keep it pinched a little bit to keep it sitting on there. look at the cuts in it, they will only fit on the two bars one way, then set the other part, whatever its called with the firing pin, lol on top of the grey metal piece. Slide it in a little it will hang up. Depress one of the two levers on the inside of the action, it will move a little bit, then depress the other side and your good to go. No need to drop the trigger for this at all. Installation is the exact opposite of removal.