Depowering a H20
the best way to depower the H20 on the water is to reduce rotation of the mast. you can additionally close the slot between the jib and main.
If you have a furling jib you can always furl it first.
on shore you can tighten diamond wire tension.
if the boat is not assembled for sailing you can increase spreader rake to help depower the boat. However I have found once you get the boat handling the way that works the best for your crew weight and experience then leave the spreader rake alone and use the other adjustments.
the best method is to take a tune up lesson from an expereinced H20 driver and have him walk you thru the various ways of setting up your boat to acheive the most preformance from it for your skill level. All the skippers I know are more than willing to assist a newer one.
You don't say where you are located but there is probably a local Hobie Fleet or sailor that can help. Let me know where you are and I will try to help you find one.
enjoy the boat