How to change root login password

how to change root login password??

I have tried as the link above but got this

exars@exars-IStNX3-15HP038:~$ swiflash -m wp76xx -r
Detecting USB of the target
DONE
Communicating with the target
DONE
Downloading the firmware
....ERROR: Firmware Download failed. Callback status 59399DONE
ERROR: Firmware Download Failed

How to fixed it??

you need to downgrade to R12: