You can do it yourself with the right tools and knowledge. Then you will know it's done right and you save a lot of money.

To repair or change a faucet, you have to turn off the water. When working on a sink or lavatory faucet, you should be able to do this by turning cutoff valves installed in the supply lines below the faucet. Sometimes, though, those valves themselves wear out and need to be replaced. Occasionally they may not have been installed in the original work. If they aren't there or need replacing, do that first.

When you buy your new faucet, consider getting new supply lines. Those are the tubes that connect the cutoff valves to the faucet. If the connections on the new faucet aren't located in the exact same place as the ones on the old one you will have to replace the supply lines. You may want to replace them even if the connections are in the same location. It can be difficult to get the old lines attached to the new faucet without having a leak from the line or the connection. Be sure to get the ones for faucets and to make sure you have the proper fittings to attach them to the cutoff valves -- threaded or compression.

Before you close the cutoff valves, you may want to drain the pipes. If you can open the faucet you're going to replace and open another one on a lower level, do so. Wait for the upper faucet to stop running and then close the cutoff valves. If it won't stop, you can either live with the little bit of water left in the supply lines or turn the water off at the main cutoff for the house and then at the cutoff valves. Once they're off, close the downstairs faucet and open the main cutoff if you need to.

If you decided to replace the supply lines, remove the old ones from the cutoff valves first. An adjustable or open-end wrench on the fitting that connects the supply line to the cutoff valve should do the trick. If it's really hard to turn use a pair of adjustable pliers to hold the cutoff valve steady so that the torque will not damage it or the connection between it and the supply pipe from the wall or floor.

To detach the supply lines from the faucet, the best approach is usually to lie on your back so that you are looking up at them. If you can get your adjustable wrench on the nut that attaches the supply line to the faucet and turn it, do that. If the space is too narrow for an adjustable wrench then you need to use a basin wrench.

If you're replacing the supply lines set the old ones out of the way. If you're going to use the old lines to supply your new faucet, gently push the top end aside for now.

Removing the old faucet definitely requires a basin wrench. The mounting nuts are tightened to the underside of the sink or lavatory. Turn the head of the wrench so that its jaw will tighten as you turn the wrench counterclockwise. Then set the movable arm of the jaw around the nut and turn the wrench. Take the nuts all the way off, then crawl out and lift the old faucet off. If it seems stuck, rock it side-to-side or front-to-back to break the seal and any old putty loose.

Clean the area where the new faucet will sit. Thoroughly. Once the area is clean and dry,  look for a gasket that may have come with the new faucet. If there is a gasket, lay that in place. If there isn't a gasket, form a narrow "cigar" of plumber's putty by rolling it between your hands. Lay the "cigar" on the mounting surface where the edge of the new faucet will be. Set the new faucet on the gasket or the putty. Stabilize it there and crawl back under to mount it.

The faucet will have one or two mounting stems, depending on whether the water enters it at each end or in the center. In either case, slide the new washer(s) over the stem(s) and run the mounting nut(s) up until it is, or they are, hand tight. Crawl out long enough to make sure that the faucet is still where you want it to be. Then go back under and tighten the mounting nut(s) with the basin wrench - flip the head of the wrench over to tighten (clockwise).

Installing the new supply tubes or reattaching the old ones is the reverse of removing or detaching the old ones. Tighten the connections reasonably tight with the appropriate wrench. Then cut the water back on and check for leaks. Tighten a little more if you see any.

That's it! Use your new faucet to wash your hands and then put your tools away.