This post will provide instructions for performing a clean install of the Windows 10 operating system using a valid Windows 7, Windows 8 or Windows 8.1 license (or OEM License). Hopefully Microsoft will provide Windows 10 as an ISO download, similar to the way Windows 8 was released, and these instructions will be similar to clean installing Windows 8.
Clean installing offers the best performance and reliability, due to the fact that you are not retrofitting a new operating system on top of all your old cruft. User profile and library directories are created from scratch and not linked/renamed, the driver cache and registry hive are cleared and start fresh…etc.
For a more detailed explanation of the benefits of a clean install, see this How-To Geek article.
All add more info as the specifics of the Windows 10 upgrade path become clear…