Here's a quick guide on upgrading to Ubuntu 19.04.

  1. Open Software & Updates.

Software & Updates

  1. Open Updates tab and select For any version near the Notify me of a new Ubuntu version.

Updates Tab

  1. Open Software Updater.

Software Updater

  1. Click on Install now.

Software Updater

  1. Click on Restart now.

Software Updater

Probably you will need to repeat 3, 4 and 5 steps few more times (is case you have an uninstalled upgrades or an <18.10 Ubuntu version):

Software Updater

Release Notes

Distribution Upgrade

About

Software Updater

Distribution Upgrade

About

That's it!