Download Ubuntu 15.04. Learn how to upgrade to Ubuntu 15.04, how to install Ubuntu 15.04. Download Ubuntu 15.04 ISO CD Images and make a Ubuntu 15.04 Live USB.
The Ubuntu 15.04 will be supported for 9 months for Ubuntu Desktop, Ubuntu Server, Ubuntu Core, Kubuntu, Ubuntu Kylin along with all other flavours.
Images can be downloaded from a location near you. You can download Ubuntu 15.04 ISOs from:
http://releases.ubuntu.com/15.04/ (Ubuntu Desktop and Server)
http://cloud-images.ubuntu.com/releases/15.04/release/ (Ubuntu Cloud Server)
http://cdimage.ubuntu.com/netboot/15.04/ (Ubuntu Netboot)
http://cdimage.ubuntu.com/ubuntu-core/releases/15.04/release/ (Ubuntu Core)
http://cdimage.ubuntu.com/kubuntu/releases/15.04/release/ (Kubuntu)
http://cdimage.ubuntu.com/lubuntu/releases/15.04/release/ (Lubuntu)
http://cdimage.ubuntu.com/ubuntustudio/releases/15.04/release/ (Ubuntu Studio)
http://cdimage.ubuntu.com/ubuntu-gnome/releases/15.04/release/ (Ubuntu GNOME)
http://cdimage.ubuntu.com/ubuntukylin/releases/15.04/release/ (Ubuntu Kylin)
http://cdimage.ubuntu.com/ubuntu-mate/releases/15.04/release/ (Ubuntu MATE)
http://cdimage.ubuntu.com/xubuntu/releases/15.04/release/ (Xubuntu)