@KattyLou 

Hi,

First of all, a TL-WPA7510 that was working fine previously shouldn't suddenly stop working because it "needs updating".

Before attempting any update try the following:

Unplug the TL-WPA7510 adapter (that's the one that is not connected to your router) from its wall socket, bring it to the same room where the TL-PA7010 (the one that connects to your router) is located and plug it into a wall socket that is close to the wall socket of the other Powerline adapter. Wait a while and then check the LED status.
  --> In case the LED now turns green (or yellowish), then then bring the TL-WPA7510 adapter back to the original location and test again what happens.
  --> In case the LED still turns red, then you might want to reset both Powerline adapters (by pressing and holding the "Reset" button on each adapter) and then set them up again using the same method you used two years earlier.

As for updating Powerline adapters.
I don't think TP-Link's Powerline adapters are supported by the "Tether" app. Supported devices are listed here https://www.tp-link.com/en/tether/product-list/ .

Powerline adapters are accessed either via TP-Link's "tpPLC" software/app or via the web management interface ( http://tplinkplc.net/ )

  @woozle 

Thanks so much for your reply.

8ve tried your suggestion but the light is still red.

The update was suggested as nothing else was working.

The method I used 2 years ago was a different router with a WPS button.

My router was changed when I upgraded to fibre around 18 months ago.

I'll call the 8nternet company and perhaps they can access the router and do something.

And thank you for the links.

That's very kind of you