I can confirm that the Xenon bulbs in my Spider are D5S (25W). Also definitely a hassle to get at without removing the wheel. You can turn the steering full lock outwards (i.e. turn right for the right side and vice versa), lift the flap in the wheel arch as per the manual. There is a round plastic cover to remove, then you can access the bulb. But with the wheel on, you are working blind by putting your hand through the flap. The bulb can be removed by turning anti-clockwise (as viewed from behind) by about 30 degrees, and the reverse to fit but you have to find the right angle to push it in by feel.
I might now try replacing with the LED plug compatible bulbs, but if I do I will remove the wheel to do so as I am sure it will be quicker overall and involve less cursing!
