Rosieres 4040F Double Oven – inside oven lights

Hi, I have a Rosieres 4040F double oven which I acquired when I bought my house. The light bulbs in both ovens have burned out and need replacing. However, I can’t work out how to remove the glass casing – does it screw out, pull out or what? I have the instruction manual which is absolutely no help whatsoever saying “to change a defective lamp, simply remove the glass housing, replace the lamp with an identical one and refit the protective glass housing”. Nothing simple about it – neither of the glass casings seem to want to budge and I am worried about damaging them if I put too much pressure on. Many thanks.