If you're using the WiFiESP library, which I recommend despite the debug output thing, then you can pass it any object you like from your sketch to communicate with the ESP8266. So no modification of the library necessary, in your case you would only need to do:
And after looking at the library source code, that is exactly what I was trying to do to the uartWifi library I was previously using.
Normally you can do an OTA firmware update using AT+CIUPDATE but I couldn't because the DOIT firmware it shipped with doesn't support that function. Since it looks like you might have an AT firmware installed you might be able to do the much easier OTA firmware update but my understanding is the AI Thnker....
I was able to upload the firmware using the tool and instructions provided through the Jaycar website along with that uartWifi library.