Turn off the water under the sink.
Remove the screw in the handle with the Allen wrench and take the handle off the faucet.
Loosen and remove the dome cap and washer under the handle by carefully turning it counterclockwise with the pliers. Take out the ball valve and stem (located in the faucet body) and remove the two seat gaskets inside the body of the faucet. Lift them out with the end of the Allen wrench.
Cover the new seats and springs with plumber's grease and push them into place in the holes in the faucet body. Place the new ball valve from the replacement kit on top of them.
Slide a new washer and dome cap on the faucet and tighten them with the pliers. Next, install the handle. If you have a new handle, install it now to replace the old one. Once it is in place, insert the screw in the hole in the front of the handle and tighten it with the Allen wrench. Next, turn on the water and test the faucet.