Here is a good little picture method for changing your cabin filters. it's good for the A4 units and the new bettle.
http://www.mann-hummel.com/mf_prodkata_all/einbau/HBAGWyte4Ub.pdf
Jeff
http://www.mann-hummel.com/mf_prodkata_all/einbau/HBAGWyte4Ub.pdf
Jeff