Use a black light to find the stains on the carpet. Turn the regular lights off when doing this to allow you to pinpoint the exact locations.
Treat small stained areas on the carpet with a vinegar and baking soda solution. Mix 1/3 cup of white vinegar with 2/3 cups of water. Blot the area with the solution, and then sprinkle it with baking soda. Allow the baking soda to dry, and then vacuum it up.
Clean the carpet with a carpet shampoo machine. The carpet shampoo machine uses water extraction and a cleaning agent to remove the deep stains from the carpet. Follow the instructions closely on the machine before you begin cleaning.
Sprinkle the carpet with baking soda or an enzyme-based odor-neutralizing powder. Cover the carpet with the powder and allow it to sit for the recommended amount of time. Vacuum the powder up slowly to ensure that you do not leave any behind.
Call in the professionals if the smell still exists. The cat urine may have soaked into the carpet padding. You will need to replace this padding to remove the cat odor from your house.