Turn off the water valves either from under the sink or from the main water supply. Open up the faucet to let the remaining water in the tubes drain. Once the water has dried down, it is safe to start working.
Remove Old Faucet:
Bend over under your sink where the faucet is installed. Now use a wrench to disconnect the hot and cold hoses from the faucet. Use a rag to wipe up any leftover water that comes out of them.
Now is the time to disconnect the faucet from the sink. Look for the nut that joins the sink and faucet. Use a wrench to loosen and open it up. Clear away any putty or caulk using a knife. Now carefully lift up the faucet and remove it from the sink.
Clean up the area before starting to work on the new faucet.
Install New Faucet:
Read the manufacturer's instructions well before attempting to install because every faucet model has a different technique of installation. Place your faucet on the right hole in the sink. If your faucet comes with a gasket to seal the hole, install it first. If it does not than apply putty to the base of the faucet before installation so that water does not leak through it . Use the wrench to tighten the nut that will hold the faucet to the sink. Now that this connection is secure, you can now work under the sink.
Bend over and connect the cold and hot water hoses to the right faucet valves, hot water on the left, cold water on the right. Tighten with the wrench. When you are done with this, open up the water supply and check for any leaks.