In general, upgrading DotNetNuke is a straightforward process. It is accomplished simply by copying the files for a new version over the top of an existing version and allowing the application to guide you through the upgrade. Having said that, there are of course lots of specific scenarios, consideration of 3rd party or custom modules, high traffic sites, etc. And so any extra steps in the upgrade process are in consideration of your site's particular circumstances. But it is important to understand that the basic approach to upgrading is as simple as copy & replace.