There is no capability of updating 7970 firmware. That is only available for 6770 and 9070 di2 versions. They use the newer E tube wiring and setup. If you're not happy with the shifting speed of your 7970 di2, then you may as well give up. I've got a bike with 7970 and one with the newer ultegra 6770 with the latest firmware, and apart from the multishift on the 6770, there is no difference in shifting speed that I can discern.
Thanks for the info. I am not unhappy with my current shifting. A tech in a local bike shop said there was a firmware update for my groupset. I did a Google search and could not turn up anything for the 7970 setup. You confirmed this.