The rear ones are pretty simple. The brackets are held on with a single bolt. Once removed, the bracket will tip down, and toward the front of the car. The front of the bracket is a "T" that fits into a slot in the frame. Just rotate it 90 degrees (left or right) and it should pop right out.
Install the new bushings on the bar, and replace the bracket in the same way you removed it. Assuming the car isn't rusty, it should be a pretty quick (and accessible!) job.