Flash files are used for do software or update mobile old firmware. The latest flash files of nokia lumia 1320 has been released with its latest updates. If you want to flash this mobile you can use flashing tool phoenix service. If your mobile can't support for usb data cable you can't flash it with flashing tool phoenix service. You can use ufs flashing box for flash mobiles. It is not easy for you.
Before flashing you will need to take backup of your important data like images,messages and contacts. After flashing you will lose your all of data and your mobile will restored in its original settings.
You can download latest flash files of nokia lumia 1320 from provided links.