format of lists

[Tom C]

I have a long word document that I'm trying to reformat.
When it was created, the creator did not autoformat,and
I'm going back to format some lists. I'll highlight the
list, right click, go to Bullets and Nubmering, select the
Numbered tab, the format I want, and click ok. Then word
converts the list into an outline numbered, and I have to
repeat the steps above in order to get what I originally
selected.

Why is this happening, and how do I fix it?

Thanks,
Tom