Upgrading from Ubuntu 9.10 to 10.04 like always, is pretty straight forward. I like to use
do-release-upgrade instead of
upgrade-manager -d since (at least last time I checked)
update-manager -d does not save the downloaded packages if the download process gets interrupted by a broken network connection. Even though
do-release-upgrade does everything you need I decided to make some changes to my sources.list file so that I'm able to upgrade from a local Macedonian repository (you can get the ISO image from there too).
All I did was change karmic to lucid in
deb http://mirror.on.net.mk/ubuntu/ lucid main restricted universe multiverse
deb http://mirror.on.net.mk/ubuntu/ lucid-updates main restricted universe multiverse
deb http://mirror.on.net.mk/ubuntu/ lucid-security main restricted universe multiverse
A fast and clean way to do this in vim is by typing the following
:%s/karmic/lucid (it will find/replace every instance of karmic with lucid).