How to Upgrade Ubuntu 16.04 / Ubuntu 17.10 To Ubuntu 18.04
On Ubuntu 16.04Search Software & Updates on Unity dash
In the Software & Updates, go to updates tab and set Notify me of a new Ubuntu version to For long-term support versions.
On Ubuntu 17.10Search Software & Updates on Activities
In the Software & Updates, go to updates tab and set Notify me of a new Ubuntu version to For any new version.
Before upgrading you need to install the last update for current version of ubuntu (16.04/17.10). To install last update follow this command.
and reboot your ubuntu after update done
After reboot done, To begin the upgrade you need to start sofware updater,
Follow this for Ubuntu 16.04
Follow this for Ubuntu 17.04Press Alt + F2, then type update-manager -cd in the command and then Enter.
wait a few minutes and you receive message Ubuntu 18.04 LTS is now available. and click Upgrade.
In Ubuntu 16.04
In ubuntu 17.10
Now click upgrade to upgrade to ubuntu 18.04
Wait software update to prepare upgrade your system until a few minutes.
after prepare done, now click upgrade to start processing upgrade.
Wait process until done,
After download package done and upgraded, click remove obsolete package.
Finaally, click restart to complete the upgrade your ubuntu.