ESP8266 Wi-Fi connection setup

Hello,
I'm using Arduino IDE GK kit w/ FW v11.0.1 along with Wi-Fi board for almost 10 years. I bought the WiFi board from a guy who set the SSID and password needed for its internet connectivity. He also set the radmon.org feed from my station. The problem is that I'd like to change the SSID and password, but IDK how to. Also, I don't want to break something and stop feeding radmon.org from my station. I'm not an IT, but if someone explains to me step-by-step how to do it, I could try. Is there a web terminal or something where I can connect that ESP8266 board and change these things? It's interesting to me also how to program it to upload to radmon.org, so one day I could fix it, if my crappy hands do something wrong.

Regards,
Emo

is this the software used ?
https://sites.google.com/site/diygeigercounter/home/gk-radmon?authuser=0

there is a link on that page to a user guide to configure it :
https://www.dropbox.com/s/frou0vsbpkomuel/GK%20Radmon%20Build%20and%20User%20Guide%20v2.2.pdf?dl=1
But probably you have an older version and much could have been changed
It seems possible to boot into "AP Config Mode" and then use your phone's browser to configure the device .