How often are you supposed to change the air filter on a Honda cbf 600?

i remove and blow out every other week....change every 4000....but that's me.How often are you supposed to change the air filter on a Honda cbf 600?Every 12 months when the bike is ready for a main service .How often are you supposed to change the air filter on a Honda cbf 600?got a k%26amp;n on my bike clean it every time i change the oil (2000miles)