For ease of demonstration we have removed the unit from the car, however, this is not entirely necessary.
You can follow here to step 3, and make this conversion with the lens in place on the fitting.

Looking at the back of the lamp-housing there are a 3 T25 screws, one in a fixed hole, and 2 securing through adjuster slots.

Observe the markings on the housing:
L/G = Link/Gauche = Left
R/D = Recht/Droite = Right

Also the tab at the base of the housing.

Remove the 3 T25 torx screws

Remember you will need to completely remove the screws from the slots.

The 2 halves just separate, then rotate by about 10 degrees until the tab locates in the other notch.

Push the housing back together again.

Retighten the T25 torx screws, note that the top screw is now in the 'R/D'position.

If you removed the unit from the car, you will need to reattach it back to the car using the 3 adjuster screws. Remember to take the car to an appropriate MOT station or similar to ensure the lights are correctly aligned.

The workings...

This works because of the internal design of the roadster projector unit.
There is a large main lens which inverts and focuses the light produced from the bulb.

Because the light is inverted by the lens, the projector must sheild the lower half of the emitted light before it reaches the lens and projects onto the road.

If you note the shape of the shield, this is how the light is angled to the nearside, it is this angle which you are changing when performing the continental conversion.