Before upgrading it is always recommended that you create a backup first.
Step 1 : Check the current version of Ubuntu
This should return an output in the following format :
Linux 3.2.0-51-generic x86_64
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 12.04.4 LTS
Step 2 : Now we need to update the package list and install the update-manager-core package if it is not already installed:
apt-get install update-manager-core
Step 3 : Upgrade to the latest LTS release of Ubuntu, using the below mentioned command. This command will open up a upgrade tool. Just follow the on screen instructions to complete :
In case you get the following message from this command, it means taht there is no newer LTS version available :
Checking for a new Ubuntu release
No new release found
But if you still want to upgrade to the latest version of Ubuntu, regardless of it have LTS (Long term support), you can use the same command but with a '-d' option :
Step 4 : After the installation is completed, it is recommended that you reboot the server and check the new settings :