how to upgrade from ubuntu 15.04 to 15.10? [duplicate]
Solution 1:
Please be aware that 15.10 is still in development. Development releases are unstable, and not suited for people who do not want to fix/report/triage bugs. If you want a stable Ubuntu version, stick to the official released versions. For added stability, choose a Ubuntu LTS release.
That said, to upgrade to a development release open your terminal by pressing Alt + F2 and type update-manager -d.
You can choose to upgrade from this window.
Or, If you prefer to do this from the command-line,
sudo do-release-upgrade -d