The same question has been asked today (by another poster) in the Other Asian airlines forum.

I can't paste the link (for some reason my internet browser does not display the thread number/ id anymore in the url - anybody can help?) so here we go again:

Basic answer would be no, you can't upgrade EVA flights with CO miles. The only possible exception would a CO issued ticket on an EVA operated code share flight. But even in this case I doubt it's possible and CO ticket on EVA flight are usually more expensive than buying it directly from EVA.