I have some of the D & M piranha 2 blade jigs, and I want to take the swivel in between the blade and head of the jig off

do you mean you want to change the "split ring"?

 

There is no swivel and you will have to replace the split ring if you take it off.  Get some split ring pliers and take the blade off if that's what you want to do.  There is no reason to take the split ring off, unless its bad.