Ubuntu recommend upgrading a Server Edition installation by using the do-release-upgrade command.
It's easy to upgrade to Ubuntu 18.04 without reinstalling the operating system.
Ubuntu provides two types of releases, one is Standard release and second is Long Term Support (LTS) release. A new Ubuntu 18.04 LTS release is available to upgrade, if you are already using an Ubuntu version.
In this context, we shall look into how to Upgrade Ubuntu 16.04 to Ubuntu 18.04 LTS.
How to Upgrade Ubuntu ?
To begin, you need to first take backup of your data and put it to safe location before start upgrade process.
Then after that, follow the steps given below.
1. Upgrade Ubuntu 16.04 to 18.04 LTS
After you have taken backup of your data, go to your terminal and execute following commands:
$ sudo apt-get update
$ sudo apt-get upgrade
Now, install the update-manager-core package:
$ sudo apt-get install update-manager-core
After that, edit release-upgrades file at /etc/update-manager/release-upgrades.
Check Prompt value and it should lts.
By this upgrader it will search only for the available LTS upgrades:
So now your system is ready to upgrade.
Fire following commands to upgrade your Ubuntu 16.04 to Ubuntu 18.04 LTS system:
$ sudo do-release-upgrade -d
Now, Upgrade process will start and take some time based on your system performance and internet connection speed.
But, no need to worry just follow on-screen instructions and It will be done.
Next, you must reboot your system once upgrade process will complete.
2. Check Ubuntu Details
So now you can check ubuntu version details using command line by fire below command:
For desktop editions go to Settings > About.
You can see upgraded version details.
That's it. Finally, you upgraded your system to Ubuntu 18.04 LTS.