As Charles has said, you should set up a multilevel list whose levels you associate with paragraph styles (one style for each level). In the article at
http://www.shaunakelly.com/word/numb...g20072010.html, the built-in headings are used as examples, but you can use any set of nine styles. You do have to make use of the built-in headings if you want to be able to demote and promote headings in Outline view.
In any multilevel list, you can change the numbering level for the current paragraph by using the shortcuts Alt+Shift+Left arrow and Alt+Shift+Right arrow, respectively. (You can also use Tab and Shift+Tab.)
Changing the numbering level doesn't work for the first item in a list, though. Press Enter to create a new numbered paragraph first.