1. Follow the inlet and outlet hoses away from the softener to where they join onto your main copper pipework. Each of these pipes will have a valve on it which will currently be open. Turn these 2 valves 90' to turn them both off.
2. In between these 2 valves on your main pipework you will see a bypass valve, this will currently be closed to make your water softener work, you need to turn this valve 90' to open it in order to get water back to the house.
3. If your water softener is plugged into the electric also switch off at the plug.