Isolate the water supply valve that is on the tube that supplies water to the tank. Empty the toilet cistern. You’ll need to take the tank off the bowl. Unscrew the water supply coupling nut underneath the cistern. Alternatively you could ask Enfield Plumbers to do the job. Undo the tank bolts which hold the toilet cistern to the bowl. If you are having difficulty apply some penetrating oil. Unhook the chain from the handle. Put the tank down carefully. Remove the spud washer and its nut from the base of the flush valve using a spud wrench. Now remove the old valve. Place the new flush valve in the valve hole and check the top of the overflow pipe is at least 1″ below the tank level marking and the opening where the handle is situated. Place the flush valve below the handle lever arm and secure it to the tank from beneath with the spud nut. With a one half of a turn past hand tight with a spud wrench or large pliers. Over tightening will crack the cistern. ( EN2 Plumbers carry all the right tools for this). Put the new spud washer over the spud nut, small facing down. Put the tank cistern on its back, place the correct washers onto the tank bolts and insert them into the holes (done from inside). Place a brass type washer and hexagonal nut onto the bolts from below and tighten them slightly, hand tight. That done, lower the tank over the bowl and set it down so the washer sits neatly over the water inlet in the bowl and the tank bolts fit through the holes in the flange. Secure the tank. Connect the water supply at the fill valve inlet. Connect the chain clip to the handle. Attach the refill tube to the top of the overflow pipe. Turn on the water and test the action and operation of the flush.