with the G&G f2000 there is no need to change the spring.
lift off the butt and tighten the spring to increase, or loosen the spring to decrease.
i'm going an extra step. quick changing the inner barre and hop up and adding/removing a silencer. the front end tear down in a single button lock. now going from a barrel that is longer then a std m4 for cqb, and a barrel for a PSG1 for long range.