Have you managed to sort this yet?
I have the same car and can confirm that you need HID D3S bulbs, the H7 halogens are for main beam.
Removing the ballasts is easy enough but the plastic light covers are very tricky. One had a missing screw when I bought the car and I managed to break the equivalent screw mount on the other side - perhaps you're supposed to remove the front wheels and wheel arch covers and maybe the front bumper too, you know how it is with modern cars!
It's doable but very, very fiddly.
Then, you can get to the back of the bulb and it's secured with a circular clip (like traditional halogens) which is quite easy to remove.
Refitting is another matter entirely, make a note of the bulb alignment as the tags are nowhere near as positive as normal halogens which are almost impossible to fit wrong, the HID bulbs by comparison feel sloppy and it's extremely tricky to get the clip to engage.
If you're lucky, it might all go together first time but don't be surprised if the lights wobble on uneven road surfaces because what you thought was correct, isn't quite seated right.
I swear these things are designed to be as awkward as possible in order to discourage DIY mechanics.........but after several attempts, I did manage it successfully.
As with halogens, be very careful handling the bulbs a) they're fragile and b) are likely to blow if contaminated with grease from your fingers.