Right. Have the riser facing away from you (grip facing you) so you can see the bolts etc.
The weight adjustment system is composed of a average looking nut that is inside a silver thread (which looks like it could be adjusted with a really big screwdriver).
Remove this (from memory, it's a 3/16" allen key). It should come all the way out easily, because it's just a locking nut. Beneath this, there is a screw which takes an allen key, and this is what moves the receiver in the limb pocket.
Turning this clockwise will bring the receiver closer to you, and heavier poundage. Anticlockwise moves it further away and lower poundage. Set as you like, then replace the locking nut and you're away!
