you can try some of those sprays available at petstore specifically designed for removing it. But in my experience not much works. and even when you get the smell out the cat will piss again in the same spot.
The only way to get rid of cat piss is to dry the area out and use an unsafe chemical cocktail of bleach, industrial deoderizer and a good mop.
You're going to want the mixture 2parts bleach to 1 parts deoderizer to 2 parts water.
You'll need a gas mask to work with that solution too. The fumes will knock you out if you don't wear one. And wear goggles too.
This was what i used to get the cat piss smell out of my basement landing. But it only worked for about 2-3days, the stench came right back. I repeated the process about 3weeks later, and did the cleansing about 4 times in a row, with 30min drying rest between. I got the smell out after that.
my cat static has this bad habit of peeing half in and half out of the litter box when it's not perfectly spotless (i'd be scooping it 3 times a day if she had her way i swear to fucking god), so i've had to search high and low for good anti-cat-pee products.
i use this stuff called 'enviro fresh's GET THE ODOR OUT'. it's $9.99 at village pet foods at church and wellesley and it works really well on surfaces (my cat is picky about textures so i've never had to use it on fabrics).
the label says it's suitable for carpets but it doesn't guarantee that it won't fuck up the colour.
was it on the floor or on carpet. Carpet will be hard. But if on the floor, nothing some regular cleaner wouldn't get rid of, unless it's hardwood and had soaked thru. In that case you may need some amonia.
you best bet is to go into the pet store. That is what they are there for.
if it's something that can be picked up and thrown in the washer then you are okay with detergent and some febreeze clean wash.
if it's carpet - that's much harder. you'll have to get a specialty product from the petstore and follow the directions. don't just febreeze the spot - doesn't work on something as strong as cat pee. make sure to thoroughly dry the spot - with a heater or a fan or something. any dampness will keep the smell and also seep into the floor below and then you'll never get it out.
hardwood you should be fine with a good cleanser and then a spray from the petstore.
As you know I have 4 kitties...A vet once told me a good way to get the smell out and it totally works. I use it all the time. You know that stuff Dettol? It's a brown liquid with a green and black label. It's an antiseptic cleaner. You can find it at Shopper's or any grocery store. What you do is mix it with water in a spray bottle(mainly water), and spray it where you need to. I swear the smell will come out if you do this. Seriously, it is the only thing that has worked for me. Good luck.