what brand weed eater do you have? Each one has it's own way to ge the bell off, then the inside is all about he same. And how you get it off depends on if you are saving it...
IF you have a ryobi in the stem jutting out of the bell you'll see a hole, in there is a small torx head nut, unscrew it and out it comes. TO unscrew it you'll need a torxhead driver, and not one with interchangeable bits. M, I didn't care about that pressed tin piece of carp, so I used a saw and cut more of the tip off, and fit my change-able tip into it, worked great.
inside the clutch are the two pieces, 2 springs a flat washer and a nut. I clamp a pair of needle nose vice grips around the swinging pieces at a point were I can easily fit them and than tap the flat washer in the direction it shows with a big screw driver and hammer. One that is loose the nut comes right off then the whole assembly slides off the shaft.
do a search for clutch removal and you should find plenty on here about it.