Using a paper towel (or a cloth towel that you can discard), press down on the spot where your cat urinated to blot up the liquid. Repeat this method until the area is mostly dry.  If the spot has happened a while ago, you can skip this step. If you have a blacklight, you can use this to find old, dried cat urine. You can purchase an enzyme-based cleaner specifically formulated for pet stains in many pet stores and online. Follow the manufacturer’s instructions. Most pet enzyme cleaners can be applied liberally to the affected area and left to dry completely. If the enzyme product did not completely remove the smell, you can try using a vinegar solution. Mix equal parts of white vinegar and water and apply this to the affected area. Vinegar will further breakdown the smell and help it to dissipate. Pour the vinegar solution directly onto the soiled area. Using a scrub brush, work the vinegar solution into the stain. Use a paper towel or old rag to blot up as much of the mixture as you can. Allow the area to dry completely, then assess if the stain is cleaned, or if further action is necessary.

Summary:
Blot up the urine if it's still wet. Use an enzyme-based cleaner. Create a vinegar solution from equal parts vinegar and water. Scrub the vinegar into the stain. Allow the vinegar solution to sit for 10-15 minutes, then blot.