the downloaded file (e.g., V8-S68AT02-LF1V198.bin ) directly to the root of the USB drive.
It is not a part of a multipart .rar archive, but rather a large .bin firmware update file.
the physical power button on the TV and plug the power back in. Release the button when the upgrade screen appears.
If you are looking for that specific version 198, I can help you:
the USB into your TV (use the USB 2.0 port if possible). Unplug the TV from power.