Easy to clean but before you start you will need some K&N oil. In Chiang Mai available at bike accessory shop, ground floor Pantip Plaza (on the corner of Chang Klan Road, Sri Donchai Road). Not sure of other shops who stock this. It comes in a white can BTW.
Don't be tempted to use other oils, it does not work! They will just block the filter...
They have the cleaning solution too but I have also used dish washing liquid.
Never use high pressure water or air on the filter. Just swish it around in a bucket of soapy water until it looks clean, then rinse well. Let it dry for a few hours in front of a fan. Apply fresh K&N oil and your done.
I think there are instructions on the K&N filter oil can as well.