Do you mean changing the retroarch hotkey button? If so you can change it in the retroarch config files. Got to this folder:
/opt/retropie/configs/all/retroarch-joypads
There should be a config for each controller.
In the config file change: input_enable_hotkey_btn = “0”
To: input_enable_hotkey_btn = “16”
Button 16 should be the home button on the PS3 controller.
