How to remove speed jump bike freehub?

[Marchaugh]

I recently purchased a second-hand jump bike, and it sometimes feels like it slips a gear although it is single speed, I think the freehub may have some issues. I've taken the wheel off and the bolt out, however, I can't see how to take the freehub off, it doesn't look like it can be done with an Allen key but I think I can see some splines. does anyone know how to take this freehub off or if it can be taken off? See the pictures attached. MT.

 

[Cycleops]

Most come off with a 10mm Allen key so give that a try, some have a larger size.