Windows 10 was released today! See some information about the upgrade to Windows 10 here:
Update installs Get Windows 10 app in Windows 8.1 and Windows 7 SP1 – describes the prerequisites for the Windows 10 update: You must have April 2014 update rollup for Windows RT 8.1, Windows 8.1, and Windows Server 2012 R2 (2919355) installed in Windows 8.1 or install Windows 7 SP1.
Via Windows Update: See How to get an update through Windows Update.
Download Windows 10 – with download of the media creation tool to download Windows for users running Windows 7, 8.1 and 10. See how: Installing Windows 10 using the media creation tool.
Windows 10 Download – Die Images sind da by Werner Illsinger (german)
For Microsoft Partners and Developers Windows 10 is also available on MSDN and in the MPN.
Happy updating!