Easiest way to upgrade to koolshare (link below) or HGG final from post 911..

https://drive.google.com/file/d/1x7qh_GovUo...lrf11-BEUW/view

1)download and flash the modified version of original tenda firmware that allow to direct flash merlin : ac18_kf_V15.03.3.7 from the link above..Then u are good to flash any Merlin based firmware without needing the hassle recovery mode method..

Please flash only firmware version based on 380.70 and below, any newer version will brick the router upon factory reset or after nvram cleared. Thus HGG final is the ideal rock stable version if u don't bother about the latest security patch.

Lastly, Flash at ur own risk!