After a brief seach on this forum, I've only found yum upgrade comments amounting to "you can use apt, see the article" or "use a CD".
However, I ran across this page:
http://www.brandonhutchinson.com/Upg..._with_yum.html
which basically says (1) replace yum.conf repositories and (2) install new fedora-release package.
Has anyone here tested this?