It looks to me like you need to loosen the clamps on the boot and slide it rearward. Then you can uncouple the U-joint from the driveline by removing items #54 and #55 in the TC30 diagram below. That will allow the U-joint to slide off the shaft and the boot will be able to be removed and replaced with a new one. I've never done it, but it looks like a fairly simple job. Uncoupling the u-joint from the shaft is probably the hardest part of the job.