After asking for your password, you will be presented with the Release Notes for the release you’re about to upgrade to.
Select the Upgrade button to start the initialisation process. A few moments later you’ll be asked Do you want to start the upgrade? Press Start Upgrade to pass the point of no return and start the upgrade process.
The upgrade will now proceed. The Distribution Upgrade pane will track the upgrade process and allow you to monitor progress. As the process is dependent on both your network connection and the performance of your computer, the upgrade could take anything from ten or 20 minutes to an hour or more.
After the new packages are installed, you may be asked whether you want to remove any obsolete packages. These are packages that were installed on your previous version of Ubuntu but are no longer required by the new one. You can safely select Remove.
Finally, you’ll be asked to restart the system to complete the upgrade.
Congratulations! You have successfully upgraded Ubuntu!