I'm using Ubuntu 15.04. I want to update to 16.04. But the Software updater does not show the required update. How do i update?
In order to upgrade your distribution you may give this a try:
sudo apt-get dist-upgrade
As the manual page itself explains:
dist-upgrade dist-upgrade in addition to performing the function of upgrade, also intelligently handles changing dependencies with new versions of packages; apt-get has a "smart" conflict resolution system, and it will attempt to upgrade the most important packages at the expense of less important ones if necessary.
It'll upgrade the distro to its latest version.
First you need to upgrade to 15.10, then you can upgrade to 16.04.
From a terminal window:
sudo apt-get update
sudo apt-get upgrade
Reboot if asked.
Answer questions and reboot as required. Now you should be at 15.10
Answer questions and reboot as required. Now you should be at 16.04