Needle not centered

Question

I have been using my Janome Jem for a couple of years now-and just noticed the reason my seams are smaller than everyone elses. My needle is not centered.
How would I make an adjustment to the machine so the needle would be centered? I just checked my straight and zig zag stitches and they are off because of this, making it impossible to do some functions.
Thanks for any and all help,
Pam