k&n's cleaning kit is quite good. but the cleaning agent feels like its not much more household cleaning detergent. in either case, if you have a k&n filter, its good to use their kit as their filters aren't cheap and you can hold them responsible if anything goes wrong.
in either case, spray your cleaning agent of choice onto the filter element. let it sit for a minute. if you have lots of particles stuck on (dirt, leaves, bugs), use a soft brush (toothbrush?) to scrub it off GENTLY. then run the filter under a low pressure tap. make sure the water is flowing from the inside - out. this is so that the water is flushing dirt outwards and not deeper into the filter element. then shake the water out and leave it to dry naturally <-- this takes a long time, be patient.
make sure the filter is absolutely dry before continuing. if you have an oiled filter, you will need to spray the oil on evenly once the filter element is dried. too little oil and particles will pass through - bad for engine. too much and not enough air will pass through - bad for performance.
DO NOTs...
- using an air gun is bad. the filter element is delicate. blowing compressed air through it can damage the element. if you absolutely must, use a VERY low pressure.
- similarly, running high pressure water through the element can damage it the same way as air pressure can.
- in general, be gentle to your air filter. don't use any force.
good luck. let me know if you need any more help.