just did it a week or two ago. much easier than cutting them in half (dremel and air grinder), is to grind the heads off the mushrooms (flared part on top). then use a long punch to press the pins out. when the pnch doesnt fit through the hole anymore, i used vice grips on the pin. i hammered the vice grips, which lowered the pins.
i used two jack stangs with thick towels on them to support the door. the outer hinge held the door even with no pins. getting the old bugger bushings out can be a pain, as was pressing new ones in. they are soft, dont beat them too much.
if you find that your outer hinge (that bolts to the frame) is spread out, so that the cotter pins wont go it, use vise grips to hold the top two pieces (the pieces that the bushing is in between), and the bottom two pieces together. the frame part of the hinge will be pulled up to the inner hinge (its boxed and stronger). then slide the cotter pin in.
which reminds me, when you push the pins in, try to get the hole for the cotter pin where you want it (read: so you can get the cotter pin in). i chose to use hitch pins, as they were easier (shorter) and went in easy. will be easier to remove.
thanks to Mustang Mikey and others whom gave me advice doing this.