Update Ubuntu 14.04 to 15.04 to 15.10...

Dist-Update Ubuntu Version

Before you upgrade, you need to install these upgrade helpers:

sudo apt-get install update-manager update-manager-core
After that, go to /etc/update-manager/release-upgrades file and change Prompt=lts to Prompt=normal. Make sure that meta-release file in same folder looks like this. If it isn't there, add it at the bottom of the file:

[METARELEASE]
URI = http://changelogs.ubuntu.com/meta-release
URI_LTS = http://changelogs.ubuntu.com/meta-release-lts
URI_UNSTABLE_POSTFIX = -development
URI_PROPOSED_POSTFIX = -proposed
Upgrading from 14.04 to 15.04 will looks like this: 14.04 -> 14.10 -> reboot -> 15.04 -> reboot -> done

Here are the next steps:

execute do-release-upgrade -d in terminal
[follow screen instructions], reboot at the end. 14.10 will be installed
execute do-release-upgrade -d in terminal
[follow screen instructions], reboot at the end. 15.04 will be installed

Thanks! used in: https://gist.github.com/wellington1993/44def31e824d0b7a45fe14609738e696