Trying to Remove Old Light Switches

[pawville]

I am trying to remove two old black turn knob light switches that are mounted on the outside of the wall. The black knob unscrews easily enough but I am having difficulty removing the rubber like cover to the wiring. Is there a trick to doing this? They are mounted on a very narrow wall space between two exterior doors. It is my hope to replace it with an updated in the wall (in a proper wiring receptacle) new light switch. Any help is appreciated. Thanks.