If I recall correctly, the instructions on changing the engine air filter are in the owners manual. Even if they aren't, changing the filter is extremely easy. You just need to remove the engine cover over it, unclip the clasps holding the airbox shut, lift the cover up enough to slip the old filter out and the new filter in, and then clip the box closed.
Steps I used in replacing the dirty OEM filter for a drop-in K&N :
*Use screwdriver tip to push center of plastic clips, remove clips from the pass. side cover and the three or four from the front cover on the airbox side.
*Remove the pass. side cover
*Unlatch the 4 or 5 latches holding the upper portion of the airbox to the lower...this can be done by hand.
*While lightly prying up on the front cover, pry up the upper portion enough to remove the filter. You should be able to slide it out without removing the upper airbox portion altogether.
*Slide in new filter (Note : there is an UP and DOWN portion of the filter!)