I just recently was selling these but have never taken apart the motor housing. I think though that once you remove the screws up top then the top exhaust area should turn to loosen for you to be able to access the Muffler Batting filter inside.
Out of curiosity what is wrong with the unit? That definitely looks like a 360 newer model. Your premotor filter is brand new I see. So with new cones and motor sounding good you would have full power!!