Gently with a screw driver or pocket knife.
You will need new ones anyway. So work them off with a screwdriver. Clean the pipes up with steel wool, or sandpaper and use a bit of high temp grease to hold the new ones during the installation of the new mufflers.
Depends on the mufflers, sometimes you slip the new gaskets into the mufflers, if they do not have a lip to hold the gasket, put them on the pipes and temp use a wire tire clamped tight ahead of them to hold the gasket while tapping new mufflers on with a rubber hammer, then cut the wire tire. Gently pry the muffler clamp ends a bit wider also with a large screwdriver. That way they will slip on easy.
Use a bit of anti seize on bolts and nuts and so on.
They can get that way, hard as a rock.These things seem really stuck to the pipe.
they dont seem to want to budge!
I hope you took GatorWings advice about the gloves! That sintered metal and mineral wool sure does itch down under your skin.
Those are muffler gaskets, now you know how to remove them. There are also 6 exhaust gaskets on this bike and they can be tricky to remove as well. They are "O" shaped crush type gaskets and the old ones often look like part of the heads, but they will pry out with the aid of an awl and small hammer.