To replace a Delta faucet washer, take out faucet handle, remove the retaining screw and the nut and take the valve of the faucet out from the wall or the sink. Then, unscrew the washer stem, remove the O-ring and replace with new ones before reassembling the faucet.
Begin replacing the washer of a Delta faucet by switching off the water supply. Turn the handle of the faucet on and allow any water in it to drain.
To pry away the handle of the Delta faucet, force the index cap out using a screwdriver with a flat head or a blunt knife. Unscrew the retaining screw and pull out the handle. Next, remove the faucet using a pair of adjustable pliers to unscrew it. To take out the faucet valve, turn the nut counter-clockwise and pull it out.
To unscrew the stem washer of the faucet, use a Phillips screwdriver to take out the screw located at the base of the faucet. Cut the stem's O-ring using a blade. Discard the O-ring and the stem washer.
Now, apply heatproof grease on the new O-ring and washer and attach appropriately on the faucet. Apply the grease also on the faucet's threads. Tighten the stem screw. Avoid over-tightening, as this could distort the washer. Finally, reassemble the faucet, its handle and index cap.