Ubuntu OSアップデート

$ cat /etc/update-manager/release-upgrades
# Default behavior for the release upgrader.
 
[DEFAULT]
# Default prompting behavior, valid options:
#
#  never  - Never check for a new release.
#  normal - Check to see if a new release is available.  If more than one new
#           release is found, the release upgrader will attempt to upgrade to
#           the release that immediately succeeds the currently-running
#           release.
#  lts    - Check to see if a new LTS release is available.  The upgrader
#           will attempt to upgrade to the first LTS release available after
#           the currently-running one.  Note that this option should not be
#           used if the currently-running release is not itself an LTS
#           release, since in that case the upgrader won't be able to
#           determine if a newer release is available.
Prompt=lts

$ sudo apt-get update
$ sudo apt-get dist-upgrade
$ sudo apt-get autoremove

Ubuntu 14.04LTSから16.04LTSにアップデートする手順
Ubuntu 最新バージョンへのアップグレード