I have followed the instructions for the tutorial at http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Trace.html but when I click OK to update the Trace Bitmap, my image does not change. Am I missing a step because the image does NOT look like the Preview that I have updated. Hoping someone can help. Thanks.

Welcome to the forum!
Are you sure that you have the image selected that you want to trace? That happens to me all the time, when I'm trying various different settings and options. Somehow the image gets deselected, and when I OK the trace, nothing happens.

The other thing that might be happening, is that you don't notice the traced image, because the original remains underneath the scan(s). If it includes a lot of transparency, it might actually be there, but you can still see the original underneath, and it's hard to notice the scan. Try just moving the original away, and see if the scan isn't there all along??