In the event that was held yesterday, Windows 10 RTM version will be officially released in 2015. You can upgrade to the Windows 10 Technical Preview for Enterprise on PCs running Enterprise versions of Windows 7 (including Windows 7 SP1), Windows 8, or Windows 8.1.
Windows 10 Technical Preview for Enterprise is an new big update from Windows 8.1, it’s an early look at some of the features and functionality in store for Windows 10, the next version of the Windows client operating system. Windows 10 brings back the start menu which was removed in previous Windows release. This release improved enterprise-grade security, identity and information protection features, reducing complexity and providing a better experience for the modern needs of business.