Is there a way to access/explore (and more importantly, manipulate) WP8 system files either from a computer (Windows, Mac OSX, or preferably Linux) or from the phone itself? What I am trying to achieve is access Whatsapp's auto backups and delete them. So, if there is a way to get around that without having to access the system file, please share your knowledge.
There is currently no way to access the general file system of a Windows Phone 8 device, especially the storage used for each individual app.
The only access you have is to the Documents, Music, Video, Ringtones and Pictures when your phone is plugged into a PC.
In the case of WhatsApp, you should contact the developers and ask for a feature to clear out old backups or export them.
try the steps are in this youtube link, just copy paste system path using winRAR, when phone is connected to a windows pc -> https://www.youtube.com/watch?v=j03Q6yEi6K0