Muffler and header are one piece. Not meant to be separated. Nothing you can't do with a dremel, hacksaw, or other cutting tool, though. THen you'll have to find a muffler that fits onto your cut header and can be mounted.
Dunno what that whole thing is you ahve there, though, with the 'round' bolt... Just cut it off. You are going to need new clamps to cinch down your new mufflers to the old headers anyway.