Old Snapshot Deletion Errors

I have a similar problem that I'm struggling to get past at the moment. My 314 went belly up at the beginning of the month and Netgear support had to reinstall the OS remotely and get it all working again. (OS reinstall wouldn't work for me at all). Since then, the NAS has been running reasonably well, but I have been wondering what has happened because my disk space usage has increased dramatically. In my snapshot timeline, I have snapshots from the beginning of July available. If I look in the .snapshot folders, all of the previous snapshots back until January are still in there and I can't get rid of them. I need a bit of advice on how to do it.