So, i recently updated the firmware on my Archer C20 to the latest one available and ever since then i have been facing problems  i.e: whenever my gpon modem loses signal and gains it back again my router fails to reconnect to the internet and the internet light on the router glows red instead of green. I have to manually restart the router in order for it to get internet access. HOW DO I GO BACK TO THE OLDER FIRMWARE???