Need to Delete Back Up Set on N360

I set up a back up and did not realize it would take up so much space on my hard drive.  Now I have a huge back up file I need to delete and it seems it will take years at this rate! Chat with Norton rep confirmed that they are encrypted files, so they need to be decrypted first and then deleted.  Its crazy to me that there is no warning message that prompts you about the size of the back up file that was about to be created. I had no idea what an issue it would be to delete it.

Does anyone know of an alternative for deleting these encrypted files?