Removing Headunit in A4 B5

You should have 2 slots at the bottom of the fascia, you need the special Audi/Euro keys and be very gentle with them as you can end up with the HU wedged in. They slot in with the angled sides facing inwards, you should be able to feel them lock into place, then push the HU from the back (remove the glovebox), or pull on the tape slot. Don't pull on the keys themselves as if they're not located properly you can knacker the spring clips.