If you fail to update your device via OTA, You can update your LG Viper firmware to LS840ZVI by LG mobile Support Tools now.
1)Please make sure you have backup your device first.
2)Go to Settings > Applications > Development. Select USB Debugging > OK to turn it on.
1) Download the latest USB Drivers for your LG Viper (LG LS840)
2) Download LG Mobile Support Tools Here.
3) Install LG Mobile Support Tool to your PC.
4) Launch the LG mobile Support tool from PC.
5) From LG mobile Support tools screen, choose country and model (LS840)
6) Connect your LG Viper to PC via USB Cable.
7) Click Start Updating. The tool will analyze the phone environment, i.e., check connection status with the phone. You will see the following window