If you tell me the you're facing with your TV (e.g., stuck on logo, no backlight), I can provide more specific troubleshooting steps for the DNS K55DS712. How to update the Samsung TV's firmware using a USB drive

How to update using a USB drive. If your TV is not connected to the Internet, it is a good idea to update your TV via a USB drive. samsung.com

The file you mentioned is "part2," which implies it is part of a split archive.