The on/off plastic button top has a flat side. In line with this flat side the button has a plastic spring clip which is preventing the button from moving upwards and out. To release the spring clip you need to push a thin rod shaped object down into the small hole which is at the edge of the button on the flat side. The button top will then lift upwards. Once the button top is removed there is a screw that allows you to remove the switch mechanism. The screw is a star type head.