hi guys, i keep my time machine backups on an external hard drive. in the past year, i've gone through 3 mac notebooks and all have a backup on my external hard drive. i was wondering how to delete all the time machine backups and start fresh? i tried just deleting the folders and they went to the trash for my external hard drive but i can't delete them from there nor can i restore them - says "The operation can't be completed because backup items can't be modified." help please?