Remove old backup sets

I've had Norton 360 for many years on three different computers. I have backup sets on a few different hard drives that I want to delete but the system won't let me even as the administrator. When I use Norton to remove the sets it goes excruciatingly slow (2-3 files a minute) the backup sets are usually 150,000 plus files (do the math). it only took 15 minutes to create the sets. How do I recover all this wasted space short of reformatting the drives.