If its a Xsara not picasso, remove passenger foot-well cover which is held in with 3 torx plastic screws. As you look up into car you will see 3 cross head screws, remove these and filter is there. Ensure that when replacing filter it goes in the same way round as it came out. replace screws, job done. takes approx 15-20 mins
Mark Allison, August 2009