Begin by completely clearing out the cabinet under the kitchen sink to create ample working space. Place a bucket directly underneath the faucet's water connections to catch any dripping water. Lay down several old towels to absorb any spills. Locate the two water shutoff valves, one for hot water (typically on the left) and one for cold (on the right). Turn the handles clockwise until they are fully closed. Once closed, turn on the old faucet handles to relieve any pressure in the lines and confirm that the water flow has stopped completely.

Position your bucket under the supply line connections. Using a basin wrench for hard-to-reach nuts or an adjustable wrench for accessible ones, loosen the coupling nuts that connect the flexible supply lines to the threaded tailpieces of the old faucet. Turn the nuts counter-clockwise. Once loose, you can usually unscrew them the rest of the way by hand. Be prepared for a small amount of water to drain out. Let the lines drop into the bucket.

Using the basin wrench, locate and loosen the mounting nuts that secure the old faucet body to the underside of the sink. These can be plastic or metal and are often corroded and difficult to remove. If there is a separate side sprayer, you will also need to disconnect its hose from the main faucet body and unscrew the nut holding its base in place. Once all nuts are removed, the old faucet assembly should be free to be lifted straight up and out from the top of the sink.

With the old faucet removed, use a plastic putty knife to gently scrape away any old plumber's putty or sealant from the sink surface. Spray the area with an all-purpose cleaner or a mineral deposit remover and scrub thoroughly with a non-abrasive scrub sponge. Wipe the area clean and dry it completely with paper towels. A clean, smooth surface is essential for the new faucet to seal properly.

Unpack your new faucet. If it comes with a base gasket, place it over the faucet holes. If not, apply a 1/4-inch rope of plumber's putty to the underside of the faucet base. Carefully feed the faucet's tailpieces and any attached hoses down through the correct holes in the sink deck. From underneath the sink, slide on any supplied washers and thread the mounting nuts onto the tailpieces. Hand-tighten them to hold the faucet in place. Install the side sprayer base in its hole, feed the hose through, and secure it with its nut from below.

From under the sink, attach the hot and cold water supply lines to the corresponding faucet tailpieces (hot on the left, cold on the right). Hand-tighten the coupling nuts, then use your basin wrench or adjustable wrench to give them an additional quarter to half turn. Do not over-tighten. Connect the other end of the supply lines to the shutoff valves if you are replacing them. Connect the side sprayer hose to its designated port on the faucet body, often a quick-connect fitting.

Slowly turn both water shutoff valves counter-clockwise to turn the water back on. Use your flashlight to carefully inspect every connection point: where the supply lines meet the shutoff valves, and where they connect to the faucet tailpieces. Also check the base of the faucet on top of the sink for any water seepage. Place a dry paper towel under the connections to make tiny drips more visible. If all is dry, turn the faucet handles on, test both hot and cold water flow, and operate the side sprayer. Perform one final check for leaks while the water is running.