If you own an Elna Air Electronic and blow a lightbulb then here is the instructions to change it. The lightbulb will be a bayonet fitting 15w but maybe remove old one first to make sure you get the right length bulb at the shop.
Firstly unplug the machine. Take your mini screwdriver that came in your kit and look at the top of the machine above the needle. There is a little hole there, put the screwdriver into the hole and push down on it, this lowers the bulb holder in the head of the machine down below the casing on a slant towards the back of the sewing bed, its spring loaded so you may need a second pair of hands to do it the first time.
Hold the screwdriver down, and grasp the bulb, push it up and twist anticlockwise to undo the bayonet fitting. Push down and repeat the process to insert the new bulb, turning clockwise to insert it into the bayonet fitting. Release the screwdriver and the bulb holder will retract back into position.
If you have a Stella air electronic then it is very similar except for the location where you need to push. On the Stella look at the rear of the machine head above the bobbin cover and you will see a little slide mounted right at the end of the rear casing. Same thing but for these, put the screwdriver across the top of the slide horizontally, then push down on it to lower the bulb mounting.
That's it! Happy sewing.