yes, you can change it yourself. I changed mine myself. I'll try to explain how..
Like lovely Charlie said, there's a access flap under the front bumper (directly under where the fog light lives), pull this flap down and shine a light through to hatch to see where the fog light sits (from behine the fog light).
You will see a nut underneath the back of the foglight unit (bit of a tricky angle)
You will need a socket/rachet thingy (prefereably one with a short arm) to unscrew the nut.
When the nut is undone, you can poke the fog light unit out through to the front of the bumper.
With the foglight now popped out through the front of the bumper, take hold of it, you will see a lead attached to the back (with a yellow plug)
Pull the lead off carefully and then attach this lead to your new foglight unit.
Poke your new fog light unit into the fog light cubby hole, sit it in nicely, and now screw it back in using the socket rachet thing, then push the access flap back up.
it is literally a 5 minute job. but i had to jack my car up first because it was too low.
i know, i have no pictures to help illustrate but seriously, i got quoted £20 by Citroen and thought no way am i paying that. You can honestly do it yourself.