Remove the Barrel Clip ( ``U´´ Shaped Part )
Turn the barrel out of the Hop-Up ( Chances are the Hop-Up Buckling will stay in the Hop-Up Element )
If the Buckling should come out with the Inner Barrel, be careful not to loose the Nubbing ( Small little hose looking part )
The small brass ring is a Spacer, not required in all Hop-Up elements, don´t be surprised if there isn´t one one your gun.