How to disassemble free hub shell?
On the hub side of the freehub, there should be a Allen headed bolt that you need to unscrew.  Some are 8mm, others are 10mm and some are 11mm.  11mm is a hard to find Allen wrench, so hopefully it's 8 or 10mm.
Put the Allen wrench into the center the freehub and unscrew in the normal direction (CCW).