This TP-Link router provides no way to flash the firmware via the web interface. Therefore we simply need to TFTP the upgrade file to the router.  Ensure any firewall on the computer is temporarily disabled and follow the below:

• Please install the following TFTP software - http://kin.klever.net/dist/pumpkin-2.7.3.exe or equivalent for MAC.
• Download the firmware file from the portal as normal and save to your desktop
• Open the Pumpkin TFTP application
• On the Options page, browse to your desktop folder for TFTP filesystem root and set Give all files under Read Request Behaviour. Press OK to save.
• Turn off the power on the back of the router
• Set your computer's ethernet adaptor to use a static IP of 192.168.0.66, subnet of 255.255.255.0
• Plug an ethernet cable in from your computer to the Ethernet (LAN) Port 1 on the router
• Press and hold in the Reset button and turn on the router.

Within 20 seconds of powering on you will see the firmware being transferred in the TFTP software. The firmware on your router will be upgraded and the device will automatically reboot once done.

N.B. Occasionally TP-Link use the IP of 192.168.1.66 instead of the above. If you are unable to get the above process to work, please try again with this IP instead.