Locate the interior shut-off valve for the outdoor faucet, which is typically found in the basement, crawl space, or a utility room directly behind the exterior spigot. Turn the valve handle clockwise until it is fully closed. If there is no dedicated shut-off, you must close the main water valve for the entire house. After closing the valve, go outside and open the spigot to drain any remaining water from the pipe. Place a bucket under the interior valve if it has a drain cap (bleeder valve) and open it to drain residual water from the indoor pipe section.

From inside the house, place one pipe wrench on the faucet's connection point to the pipe. Place a second pipe wrench (or adjustable wrench) on the connecting pipe fitting to hold it steady. This is crucial to prevent twisting or breaking the pipe. Turn the wrench on the faucet counter-clockwise to unscrew it from the pipe. It may require significant force if it's old and corroded. If needed, apply penetrating oil to the threads and let it sit for 10-15 minutes. Once loose, continue unscrewing by hand. After it's disconnected from the inside, pull the old faucet out from the exterior of the house.

Measure the length of the old faucet from the connection point to the exterior flange. If upgrading to a frost-proof model, measure the thickness of your wall from the interior pipe fitting to the exterior wall surface. Purchase a new frost-proof sillcock of the correct length (e.g., 8-inch, 10-inch, 12-inch). The new faucet must be long enough to extend through the wall and connect to the pipe. Clean the threads on the interior pipe fitting using a wire brush to remove old pipe dope, tape, and any corrosion. Ensure the opening through the wall is clear of debris.

Take your new faucet and wrap the threaded end with 3-4 layers of Teflon tape. Wrap the tape in a clockwise direction as you look at the end of the fitting; this prevents the tape from unwrapping as you tighten it. Alternatively, apply a layer of pipe joint compound (pipe dope) to the threads. Insert the new faucet from the outside of the house through the wall opening until the threads meet the interior pipe fitting. Make sure the spout on the outside is oriented correctly (pointing downwards) and that the faucet body has a slight downward pitch to allow for proper drainage. From the inside, hand-tighten the faucet into the fitting. Then, use a pipe wrench to tighten it securely. As before, use a second wrench to hold the pipe fitting stationary to prevent damage. Do not overtighten; it should be snug plus about a half to a full turn.

On the outside of the house, ensure the faucet's mounting flange is flush against the siding. If the new faucet came with mounting screws and you have a suitable surface like wood or fiber cement siding, pre-drill pilot holes and secure the flange with the provided screws using a drill or screwdriver. This prevents the faucet from moving and stressing the pipe connection. To weatherproof the installation, apply a bead of exterior-grade silicone caulk around the top and sides of the mounting flange where it meets the house siding. Leave the bottom of the flange un-caulked; this creates a weep hole to allow any potential moisture that gets behind the flange to escape rather than being trapped in the wall.

Ensure the new outdoor faucet handle is in the closed position. Go inside and slowly turn the interior shut-off valve counter-clockwise to restore water pressure to the line. Listen for any hissing or sounds of running water. Carefully inspect the new threaded connection point inside the house for any drips or moisture. Use a dry paper towel to wipe the joint, as this will make even the smallest leak immediately apparent. If there are no leaks inside, go outside and open the faucet to test its operation. Let it run for a minute to flush the line, then turn it off completely. Go back inside and re-check the interior connection one last time to ensure it is 100% dry.