Jun 7, 2017

do-release-upgrade vs 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. So, dist-upgrade command may remove some packages. The /etc/apt/sources.list file contains a list of locations from which to retrieve desired package files. See also apt_preferences(5) for a mechanism for overriding the general settings for individual packages
In order to upgrade Ubuntu to a newer release you have to run in terminal
sudo do-release-upgrade
Upgrade the operating system to the latest release from the command-line. This is the preferred command if the machine has no graphic environment or if the machine is to be upgraded over a remote connection