At first you need to confirm that /etc/update-manager/release-upgrades
file has the following line:
Prompt=normal
If Prompt has any other value e.g. lts or never, change it to Prompt=normal.
Now you can run the following command to upgrade your Lubuntu 14.04 to Lubuntu 14.10:
sudo do-release-upgrade
References :
http://askubuntu.com/questions/423942/change-password-on-root-user-and-user-account