Update Ubuntu 14.04 to 15.04

Currently I have Ubuntu 14.04 in my laptop and now I want to update it to 15.04. I have Windows 8 and Kali Linux along with my Ubuntu. How should I update my Ubuntu to 15.04 without losing my other operating systems. I was thinking of downloading Ubuntu 15.04 and then installing it over Ubuntu 14.04, instead of updating Ubuntu 14.04 via terminal or update manager. Will that be a good option?

(Moreover I cannot update my Ubuntu via terminal or update manager as I use internet through a proxy server which requires authentication. I asked about it in my previous question and none of the techniques given by others worked)

Thanks in advance :)

Directly upgrade to Ubuntu 15.04 from 14.04 is not possible, but this does not mean that you can't do this. No USB sticks etc. needed. I do the update through SSH from remote PC :)

Note:

Please keep in mind, that all operations below should be completed under root permissions or sudo, as you are modifying system settings.

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

Enjoy! :)

P.S. All data and software will be preserved. Also after the upgrade don't forget to update custom apt repositories, as they probably will be disabled for the upgrade period.