Turn off the faucet water supply underneath the sink.
Lift up the handle to release all of the water from the pipes.
Slide an Allen wrench -- sometimes called an Allen key -- into the small hole underneath the handle. Turn it counterclockwise to remove the screw. Pull off the handle.
Wrap the ends of adjustable pliers with tape to protect the plastic cap ring underneath the handle and turn it counterclockwise to remove it.
Lift off the plastic cam and packing, and lift up the ball. Inspect all the parts for cracks or broken components. Remove the seats and the springs, and replace parts as necessary.