I couldn’t find any info on this on the internet, and the French version of the user manual doesn’t have any info on this simple task either, so once I worked it out I figured I might as well post a howto here.
First, you need to remove the small plastic cover directly below the instrument panel (just below the speedo/tacho). It is held in place by two plastic lugs on either side. Unscrew these and remove the cover. Things are annoyingly tight and fiddly in here. You need to pull back the circular rubber cover over whichever side you need to get at. It should have a tab that you can grab to pull it back. Once you do that, you will be able to see the back of the headlight assembly. Grab the black plastic part and rotate it, on mine it’s in an anti-clockwise direction (you might need to push the handlebars to the other side in order to have space to get your hand in). It will rotate about 45 degrees and be released from its restraints. You can then pull it out, remove the wires. On mine, looking from the back, I have green, white, blue in a clockwise direction. These are just slide-on, so you can just pull them off to better get at the assembly.
To remove the bulb you need to push it in, and rotate it, I think anti-clockwise. Replace the bulb and reverse the above instructions to get everything back together. Hope this saves someone some time.