I have an LG 47G2 Google TV running Android 4. I found out how to enter the recovery mode for the TV.
Unplug the TV and plug it back it to keep it at shutdown.
Press and hold the Settings button.
Press and hold the Channel Down button.
Release the Settings button then the Channel Down button. (Not at the same time)
My question is how do I update Android via the Android Debug Bridge in recovery?
Just because you can access Android recovery. Doesn't necessarily mean you are going to be able to install any usable update. Without unlocking the OEM bootloader and or rooting your device or being able to load TWRP, and then a custom ROM intended for your device. All you are going to be able to load is signed ROMs made by your manufacturer specifically for your device. Such signed ROMs would already likely be available through an OTA update.
I would check XDA forum in the Android tv section to see if any roms exist for your device, you can't just install any ROM.