Updating the kernel in ubuntu
For older Ubuntu releases which have reached end-of-life, you can install Aptik from the DEB files linked below.
This may be useful for testing both the upgrade process and the features of 16.04 itself in advance of the official release date.
This guide will explain the process for systems including (but not limited to) Digital Ocean Droplets running Ubuntu 15.10.
Warning: As with almost any upgrade between major releases of an operating system, this process carries an inherent risk of failure, data loss, or broken software configuration.
Before upgrading, consider reading the Xenial Xerus Release Notes.
Before attempting a major upgrade on any system, you should make sure you won't lose data if the upgrade goes awry.