Remove the cocking knob at the back of the gun, its just under the bolt. It should be brass and a 3/16 allen key is used to adjust it, turn it clockwise to up the velocity.
The upper tube is where the bolt/paint goes, the lower tube houses the valve, hammer, springs and adjuster.
Everyone says "Well maybe i'll make a difference",
Thinking they've got plenty of time
But you're squeezed a little tighter everyday
Finished before you can commit a crime