unclip the dial surround (thin summat under bottom corners
help) but dont let it twist too much if you can or you'll pop out the clear plastic that directs all the light
couple of screws at the bottom to release the tray/window switch panel
then you can either reach in blind and try and unclip the white shroud from the back or undo all 4 screws and push the heater panel in and down to get better access
either way it's a small 1/4 capless bulb (1.2w?) inside the shroud
iirc you can get higher wattage (brighter) versions too