Woofer in N/S/F door stopped working

Recently I have noticed that the woofer had stopped working on the front passenger door. The car has the uprated Canton sound system installed from new. Can anyone tell me just how you get the door card removed in order to access the speaker, as I'm guessing that is where the problem lies. A couple of years back I was sideswiped by a Lorry on the M25 and that door received some damage, so I'm kind of hoping that when they repaired the door, that maybe the speaker connections were not properly made and that it has become disconnected?

What tools do I need to access the fixings on the door card, I don't want to risk damaging it at all by not knowing what tools are needed or where to apply them in order to ensure safe removal and refitting of the door card.