inside the bolt.
Take the metal strip on the side off when you do this, not like in my pics where that piece is still on.
Take the bolt out of the gun and turn it upside down and you should see this:
Loosen the set screw in the back in the red circle, dont take it out, just loosen. take out the green screw up in front.
turn it over
There is a retaining ball on the inside in the red circle, but just pull forward (its 2 parts, the split should be obvious) and the 2 parts should come apart. the retaining ball might jump out, dont lose it. then take the front part away, look down into the back part and there should be a screw(on the inside, at the yellow cross area). tighten to increase fps, loosen to lower fps. then put it all back together.