Netgear R6220 can be updated directly via GUI (factory image)
YouHua WR1200JS can be updated in two steps.
 - enter router flash webpage and flash "kernel" image (use chromebrowser and let translate Chinese to german via google)
 - let reboot router and ssh into it on 192.168.1.1.
 - scp sysupgrade image to /tmp directory on this router and start sysupgrade -n sysupgrade.bin