Actually a quick web search found the following:
You might wanna check your owner manual as well.
A K&N filter is a air filter that provides better airflow than stock paper elements. It helps your engine breathe better(suck air in better), and can thus produce more power. More power can increase your fuel milage a slight amount, but only if you keep off the ole lead foot, which is hard when you get more power. Any Pep boys, autozone, O'reilly or other auto parts store should carry them.
Also consider removing the intake snorkle/silencer in front of the airbox will improve airflow.