First you need to isolate the cold water to the cistern. You may have an isolating valve on the pipe work to the ball valve. Using the screwdriver turn the slot in the isolating valve, this wants to be turned quarter of turn so the slot is horizontal to the pipework. If you do not have an isolating valve then turn the water off at the mains stop tap

Now flush the toilet, this will confirm that the water has been isolated correctly, this will also empty the majorly of the water from the cistern.

Using the pump pliers grip the bottom of the ball valve on the thread, take the adjustable spanners, and undo the nut. Once you have removed the nut, loosen the retaining nut which holds the ball valve in place, have the bowl ready to catch any water remaining in the cistern.

Now remove the ball valve, you also need to remove the red fibre washer from the tap connector, replace this with a new fibre washer.

Insert the new ball valve and wind on the retaining nut, using the pump pliers grip the thread lightly and tighten the retaining nut with the adjustable spanners.

Next wind on the nut from the tap connecter, using the pump pliers hold the thread and tighten the nut with the adjustable spanners. Turn on the water and check for leaks.