Under the hood, there have been updates to many core packages, including a new 3.19-based kernel, a new glibc, and much more.One of the larger changes this cycle is a switch from upstart to systemd as the default for managing boot and system service startup.
Ubuntu Desktop has seen incremental improvements, with newer versions of GTK and Qt, updates to major packages like Firefox and LibreOffice, and stability improvements to Unity.
Ubuntu Server 15.04 includes the Kilo release of OpenStack, alongside deployment and management tools that save devops teams time when deploying distributed applications – whether on private clouds, public clouds, x86 or ARM servers, or on developer laptops. Several key server technologies, from MAAS to Ceph, have been updated to new upstream versions with a variety of new features.
Take a backup of your data on to the external device like USB device,Hard disk or CD/DVD
Desktop upgrade from Ubuntu 14.10 (Utopic Unicorn) to Ubuntu 15.04 (Vivid Vervet)
Open the "Software & Updates" Setting in Systemsettings.
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 ‘15.04' is available.
Click Upgrade and follow the on-screen instructions.
Server upgrade from Ubuntu 14.10 (Utopic Unicorn) to Ubuntu 15.04 (Vivid Vervet)
Install the update-manager-core package if it is not already installed using the following command
sudo apt-get install update-manager-core
Make sure the /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.
Note :- There are no offline upgrade options for Ubuntu Desktop and Ubuntu Server.