Why You Should Perform Clean Installs, Not Upgrades
 

Whether you’re installing the latest version of Windows or upgrading your Linux distribution, most geeks agree that you should probably perform a clean installation rather than try your luck with an upgrade.

New operating systems versions want to reduce the pain of upgrading and offer to bring your old files, settings, and programs along with you through an upgrade, but this can often cause problems.

http://www.howtogeek.com/142743/htg-...-not-upgrades/