Turn off the water then open the valve for that faucet and one lower down on the same run, if possible. There should be a winter shut-off fairly close, and if so, shut the water off here. Use a tubing cutter and cut the copper pipe back about a foot inside the house. Pull the old faucet out of the wall from the outside. Assemble your new faucet with a copper pipe stub somewhat longer than the old one. Measure the old one from the back of the flange to your cut, then cut the new one to the same length less 1/8" for a coupling. Slide the new one thru the hole in the wall then solder the new copper pipe to your old run, using a coupling. Be sure to follow proper procedures for soldering, sand or wire brush to bright metal, flux, etc. By the way, you might want to check the plumbing supply house in your town that advertises they stock obsolete fixtures. Check your newspaper for recent inner city murders and it is the one that is closest. Pull the stem out of your old faucet and take it to them to see if they can replace it. This is a lot easier than changing out the faucet. When it is fixed--either method--be sure to close the winter shut off in the fall and open the outside faucet. Do the reverse in the spring. This keeps water from freezing in the outside valve and destroying the seals when it expands.