I'd be surprised if the lower ones are worn, I think I've only ever done those on two vehicles, both were heavy towing use. Plenty of top ones - get new nuts & bolts as they're most likely seized in place - my preferred method was to drill out the head of the bolt to the point where it could be removed, then tighten the nut on the other side to draw the bolt out of the bush, once it bottoms out, use a sleeve or larger nut as a spacer and repeat until the bolt is out.