Hi! You can use the "sure app" if you are on Android and once downloaded to your smartphone activate the location option on your smartphone and connect it to the home network where the CX tv is connected, open the "sure app" and hit add new device, select TV, select LG, then pairs with the CX by inputting in the "sure app" the code that appears on TV and confirm. Restart the process of unzipping the software update file.zip, go to the unzipped folder, copy the only file in that folder with the " .bin" extension, past it in a folder name LG_DTV that you have created in the root of your usb drive, if you want you can rename that usb drive "UPDATE" I do not think its necessary but give it a try, then plug the USB drive in the usb port on the back of your Tv, then go to the "sure app" hit "LG TV" then hit the checkered square in third position from the right, and scroll down to the bottom end, you will see the "software update" option, hit the "software update" option, and finish with your original Lg tv remote, browse to the file location on your usb drive and proceed to the downgrade or update, if all works the tv will reboot or it migth ask you to restart the tv once you confirm, then turn off if asked, wait 5 min then start the TV and let it set the web os, then agree to the user agreement and set your tv, enjoy and come back to say that your are lucky ?
NB: I tried the "software update" option on my tv nothing happened, but I had no usb drive with firmware plug to the tv, so I think it's normal behavior has it migth only works when a firmware file is detected by the TV.
Please try this now and come back to explain what happened it may be useful for base knowledge.