Windows 10 will be released soon! Microsoft: free upgrade to Windows 10 now
Below are from Microsoft website:
Windows 10 is not for all of us, but for each of us.
*It is our intent that most of these devices will qualify, but some hardware/software requirements apply and feature availability may vary by device. Devices must be connected to the internet and have Windows Update enabled. ISP fees may apply. Windows 7 SP1 and Windows 8.1 Update required. Some editions are excluded: Windows 7 Enterprise, Windows 8/8.1 Enterprise, and Windows RT/RT 8.1. Active Software Assurance customers in volume licensing have the benefit to upgrade to Windows 10 Enterprise outside of this offer. We will be sharing more information and additional offer terms in coming months.
Above are From: http://windows.microsoft.com/en-us/windows-10/about