Removing wires from a circuit board socket
Without seeing the other side, I am fairly confident that the wires have been soldered to the pcb on the other side. To remove them, you would have to desolder it. Use a clean soldering iron on the other side and pliers on the cut wire side and pull after heating it up, one by one. The plastic can be removed when all the wires are out. Clean the holes like you would any desoldered joint and you'll be ready to add new wires.