I had a few problems replacing mine - but basically once you take the nut off, there's nothing other than time, wear, old grease and road grime and yet more wear holding it on. The bolt is not threaded into the bushing, but over time it may have worn its way into the bushing - making its own thread as it were..
The bolt is threaded at one end, you should have a grease fitting (zerk) and a washer at the nut end take those three off. Press the bolt out, using something like the tool Rons50 describes. You can buy simple ones at any auto / tool store. Spray on some of that release stuff as well if you like.
Finally you have to push the bushing itself out. For this I had to find a bolt with a head that was bigger than the bushing and smaller than the hole thru the spring. Put it into the bushing and press it out taking the bushing with it.
If you look at Classicparts item number 74-057 you'll see what the whole thing looks like new. When I got them out mine looked like they'd had a major amount of wear - a real hard life.
The new ones won't revolutionize your ride, but they'll be one significant step.