There is no firmware, all the info available is here.
http://www.tp-link.com/en/products/details/?model=TL-PA211#down
I would have a play around this area to. I found having our TV plugged into the other socket deteriorated the speed, moving it to another twin plug and having nothing else in the pair with the home plug helped loads.Anything in the other sockets (I presume it's a 2 plug socket they're plugged into