turn off water.

pop the cap (H or C) from the top of each handle, you should be able to see the screw that holds the handle. Undo that and remove the handle, you should be able to see the packing nut that holds the valve to the seat of the faucet. Take it out to examine the degree of wearing. Most likely this is just a rubber washer. You can get a pack from HD with different sizes for about 5 dollars.