Measure the length, depth and width of the bathroom sink. Measure the dimensions of the countertop where the sink is located. Double check these measurements before buying a new sink and bring them with you when choosing a new sink.
Disconnect the plumbing from the old sink. Turn off the water to the bathroom and test the faucet before handling the plumbing. Before removing the P-trap, place a bucket under it to catch any water. Disconnect the water lines under the faucet.
Loosen and remove any clips under the sink attaching it to the countertop. Use a utility knife to cut any sealant or putty between the sink rim and the countertop. Lift the sink from the counter.
Install the faucet and drain assembly into the new sink. Wipe off any excess putty from the drain installation before it dries.
Apply silicone to the under side of the sink rim. Lower the sink into the countertop, being careful to not touch the silicone anywhere but the desired position. Press the sink into place firmly and wipe off any silicone that is squeezed out.
Connect the water lines and P-trap to the underside of the sink. Turn on the water and test the connections. If no leaks are found, tighten all connections and nuts. If there are leaks, shut off the water and re-install the connections.