How do you change the air filter on a citroen c4?

Fortunately I drive on sealed roads so only had to do this once so far but I'll do it shortly again

Don't remove the bonnet as some say. Remove the wiper blades, the cardboard shield across the top of the engine, the plastic bit under the windscreen that goes the full width ( about four screws) and then unclip the fuel filter (or whatever it was) to get to the black plastic box with the filter inside.

A bit fiddly - not much room there - but doesn't take too long. Worst part is putting the plastic rail back and making the rubber seal fit the bottom of the windscreen.