How to fix a NETIS wireless router by force re-flashing the firmware

Useful links:
https://ixnfo.com/en/repairing-the-netis-wf2419-firmware-via-tftp.html
https://ixnfo.com/en/starting-a-tftp-server-in-windows.html
http://netis-systems.com/Suppory/down.html .