Well, I think I looked now in the right place, because I found the answer. You can see it here
It shows how to upgrade from each Ubuntu version to the following one. In the case of the page about upgrades from Dapper to Edgy, it warns you that Edgy is beta software, blah, blah, blah, but I think the instructions will be the same after the official release, or if they change, the relevant page will be updated. As for me, I am not planning to update now, but after the official release instead, so I'll go and visit that page again one it comes out.
It even explains how you can do it with the CD in order to save bandwidth. I guess I'll be doing it this way, because I will download it anyway, to give it out to friends, etc. And besides, my bandwidth is awful.