How do you change the light unit on my citroen xsara picasso?

To change the light bulb on a Citroën Xsara Picasso, first, ensure the vehicle is turned off and the keys are removed. Open the hood and locate the back of the headlight assembly; twist the bulb holder counterclockwise to remove it. Replace the old bulb with a new one, avoiding touching the glass with your fingers, and then reassemble by twisting the holder back into place. Finally, test the new bulb to ensure it is functioning properly.