I followed these instructions to upgrade from Ubuntu 11.04 to Ubuntu 11.10.
Then again to upgrade from 11.10 to 12.04.
Update and upgrade your apt-get modules:
# sudo apt-get update
# sudo apt-get upgrade
# sudo apt-get dist-upgrade
Do the upgrade:
# sudo apt-get install update-manager-core
# sudo do-release-upgrade
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To upgrade from to 12.04 to 12.10:
Modify /etc/update-manager/release-upgrades and set Prompt=normal.
# sudo vi /etc/update-manager/release-upgrades
Prompt=normal
# sudo apt-get autoremove
# sudo apt-get update
# sudo apt-get upgrade
# sudo apt-get dist-upgrade
Do the upgrade:
# sudo apt-get install update-manager-core
# sudo do-release-upgrade
