https://wiki.ubuntu.com/DapperUpgrades?action=show&redirect=DapperUpgradeNotes

If I am reading this correctly and you are using Warty 4.10 and not
Breezy 5.10 IMHO it would be a lot easier to back up ;your /home and
then burn an install disk of Dapper 6.06 and do a fresh install rather
than fight your way through three complete distr upgrades.

Now we all know that its a good thing that a new version of ubuntu is
released every six months, so I was
wondering if its eva possible to upgrade from the CD, just like its done
from windows, retaining all your files and settings.
This would really be cool for some of us who cant stand the wait time for
online upgrading or cant even upgrade online at all.

My last upgrade was automatically notified and I could dowload as usual
with Synpatic, Probably all new upgrades will be the same.