You have to remove the faceplate, and then loosen this screw:
[ATTACH=CONFIG]579146[/ATTACH]
It's likely to take some elbow grease, make sure you use a screwdriver that fits the slot well, and take care you don't strip the screw. Once it's loose, you only have to back it off a little bit, and then work the needlebar loose. It'll probably be stuck a little, just grab the needle clamp and twist it back and forth gently, and it should loosen up. Once it is, you have to move it upwards. You're going to be limited by this:
[ATTACH=CONFIG]579147[/ATTACH]
If you move the bar too far, the thread guide will hit the bottom of the "tube" that comes out of the head of the machine. So turn the handwheel to the highest point in the stroke, move the needlebar to where it's almost, but not quite, hitting, and then tighten that screw back up, making sure that the needle clamp is still turned the right way. It should now work with 15x1 needles.
I'm new here, and I only had a couple minutes to do this, so let me know if this isn't clear enough. I'll have more time this weekend.
Rob