There are 2 holes each side of the head unit, 1 at the top, and one at the bottom.
The tools mentioned are like a U shape, and they slot in to 2 holes vertically. Once you push them in, you push each one to the edge of the head unit. This releases the catches on the side of the HU that hold it into the dash, thus allowing you to remove the unit.
Very straightforward - even a Renault mechanic could do it.
