1. Put the flat screwdriver above where the mains wire enters, and carefully push the top cover up. A small slit will appear.

2. In the slit, slide the screwdriver to the left. The slit will grow.

3. The tricky part is to push the plastic piece with the screwdriver slightly off the center outwards so that it will come loose and the cover lifts up.

Repeat at the right.

I haven't been able to do this yet without breaking one of the plastic rods (doesn't impair usage). Don't worry too much, but be careful.