To upgrade on a desktop system:
- Open the "Software & Updates" Setting in System Settings.
- Select the 3rd Tab called "Updates".
- Set the "Notify me of a new Ubuntu version" dropdown menu to "For any new version".
- Press Alt+F2 and type in "update-manager" (without the quotes) into the command box.
- Update Manager should open up and tell you: New distribution release '16.10' is available.
- If not you can also use "/usr/lib/ubuntu-release-upgrader/check-new-release-gtk"
- Click Upgrade and follow the on-screen instructions.
To upgrade on a server system:
- Install the update-manager-core package if it is not already installed.
- Make sure the Prompt line in /etc/update-manager/release-upgrades is set to normal.
- Launch the upgrade tool with the command sudo do-release-upgrade.
- Follow the on-screen instructions.
There are no offline upgrade options for Ubuntu Desktop and Ubuntu Server. Please ensure you have network connectivity to one of the official mirrors or to a locally accessible mirror and follow the instructions above.
Source : ubuntu website.