That is odd that you can't adjust them. I have a Brother machine, they make Babylock and my deco stitches are adjustable. I'm not familiar with your machine to tell you how to adjust them.
I pulled out my manual for my PC6500. All my stitches are adjustable except the width on the straight stitch and something on the buttonhole I'll never use anyway. I have to adjust them manually by pressing the width and length buttons but they have quite a bit of adjust-ability.