I've had good results with white vinegar. Soak up any wet spots, pour on vinegar, wait a few minutes and soak up as much as you can. Test in a corner first.

A good commercial product is Outright. It has enzymes that actually destroy the odor causing bacteria. There are a couple of other similar products, all work the same way. It may take a while to get all of the smell out of the carpet, but the enzymes do the trick.

I had a dog wet the back seat of my car in gallons. I tried everything I could think of to rid the car of the urine smell. I even baked the seat in the sun for a week. I finally poured Outright on it and made sure it soaked in good. After another week, the seat was dry and I could drive the car again. And I still have the car, but not the dog!