Plug the TV back in or press the Power button. Most boards will automatically detect the file; you may see the standby LED blink rapidly, indicating the update is in progress.
Download the .rar file and extract the contents. Copy the firmware file (often named SI6M33.bin or similar) directly to the root directory of your USB drive—do not put it inside a folder. Download RR8501 C031A V50 1440x900 USB rar
Once the blinking stops or the TV restarts, remove the USB drive. Plug the TV back in or press the Power button