Delete backed up files norton 360 premier v5

I currently backup to an external hard drive (Z)  - Norton set to 'automatic'.  Norton 360 backups currently use 627GB of space!  I want to delete old backups to free up this space.  When I asked Norton Support how to do this i was told to do it via 'delete backup up file..'.  There are over 100,000 files and it took 8 hours to delete 2,000 of them overnight - so based on this will take over 2 weeks to delete all files. 

Also does this function remove the file - or the backup of the file?  I ask because the first 2,000 odd files it showed as deleting were on my 'C' drive - yet my backup files are on Z drive.

Can I simply delete the folder 'N360_BACKUP' from my Z drive and simply start again? or will this cause problems?