Step One: Choose a Faucet
Select a faucet that requires the same number of openings in the sink that your current faucet has, and the same spacing between those openings.
If it doesn't, you will NOT need to cut into the sheetrock of the wall but may have to drill a hole in the top on the sink counter. This is in case you do not already have a spray hose and or a soap pump and want one on the side.
Note: For easier installation, instead of using the supply hoses that come with the faucet, consider buying flexible stainless steel supply hoses. These are more reliable and lasts years.
Step Two: Disconnect the Supply Hose and Faucets
It is smart to always wear eye protection when working on Home Remodeling Projects.
Under the sink: turn the handles of the two shut-off valves clockwise as far as you can. If there are no shut-off valves, or if you can't turn them, turn off the water where it comes into the house.
Turn on the faucets to drain water from the hoses. Use a pipe wrench to remove the hoses from the copper tailpipes under each faucet.
Use a Basin Wrench to unscrew the nuts under the existing faucets and spout - if the nuts are stuck, use penetrating oil to loosen them. Lift off the faucets and spout, and then use a Putty Knife to scrape off any Plumber's Putty or Caulk from the top of the sink.
Step Three: Install the New Spout and Faucets
Follow the instructions that came with the faucet. They give specific details for installing the spout and handles. The following are general instructions.
Insert the faucets and spout from above the sink, using plumbers putty or silicone to seal them to the surface if they don't have a sealing gasket.
Under the sink, loosely install the gaskets, washers, nuts and other hardware for the spout and faucets. Align them above the sink and then tighten them securely.
Step Four: Install the Supply Hoses
Clockwise, tightly wrap the threaded fittings at the end of the copper tube under the faucets with Teflon tape - the tape helps form a tight seal.
Use two wrenches to attach the hoses to the faucets (for a two-valve faucet) or connector adapter (for a one-valve faucet): one to hold the copper tube so it doesn't break off the faucet, and another to tighten the nut.
Place a bucket under the sink to catch leaks. Remove the aerator from the end of the spout - if you can't unscrew it by hand, wrap a rag around it and turn it with an adjustable wrench. Open the water shutoffs and turn on the faucets for several minutes to clear out any debris. Reattach the aerator.
Step Five: Remove the Old Drain Assembly
Remove old drain assembly, including the sink stopper, the flange (the collar in the sink's drain opening), the drain body (the pipe just under the drain opening) and its locknut, the lift rod that opens and closes the stopper, and the parts that attach the lift rod to the stopper.
Use the putty knife to scrape old putty and silicone from the drain opening.
Step Six: Install the New Drain Assembly
Place a ring of plumbers putty or silicone sealant around the drain opening and insert the flange from above the sink.
Under the sink, attach the drain body to the flange and then use a pipe wrench to tighten the lock nut to secure the connection. Make sure the flange is tightly seated in the drain hole and remove excess sealant.
Step Seven: Install the Stopper
Drop the lift rod through the hole in the faucet and then, under the sink, attach it to the lift rod strap (the plastic or metal strip with a lot of holes along its length) with the thumb screw or other hardware that comes with the faucet.
Above the sink, insert the stopper into the drain. Under the sink, insert the stopper's control rod horizontally through the hole in the side of the drain body and then into the hole at the base of the stopper.
Thread the end of the control rod through one hole on the spring clip, through one of the holes in the lift rod strap and then through the other hole in the spring clip.
Use the lift rod to open and close the strainer; if it doesn't open fully and close tightly, thread the control rod through a different hole in the lift rod strap.
Step Eight: Make sure Everything Works Properly
After all the other steps have been completed and all the joints are tightened sufficiently, turn on the shut-off valves. On the faucet, turn the cold water on first, slowly, just barely open it and then if the water hose or pipes jump, wait for them to quit jumping and then turn the cold water on full blast. This will help prevent any air bubbles that may in the plumbing system from causing the water to splatter everywhere when you use the water. Repeat steps on the hot water side.