If your door is a single chute door, then it likely has a programmable electronic coin mech. You'd have to ship the mech to someone to have it programmed to accept quarters or else you'd have to swap the entire door for a conventional coin acceptor (two chutes) door.
If your door is a two or three chute door, then all you'd need to do is swap out the foreign mechs for quarters mechs and change the labels inside the buttons.