In short you can't change the bushes on a Seicento rear arm, the design simply does not have provision for pressing the old bushes out and you can't purchase bushes for this purpose except from...
there is 2 different ways to change the fluid this is a drain plug on the front of the rear diff or you can take the back of the pumpkin off on the rear diff.
If you are speaking of the rear hubs. they are attacked to the swing arm, That long axle looking thing that connects each wheel to the car. The Hub bearings are relativity easy to change if you have...
I just changed the rear axle on my 94 Tercel. once you get a new axle ( suggest you get a use one because of price). There is 2 bolts that go into the frame just under the rear seat area. you then...