Free Upgrade to Windows 10: Official News: Microsoft says you can download the final version of Windows 10 on July 29. All you have to do is sign up for a “reservation” on Windows 7, Windows 8 or Windows 8.1 machines.
Don’t worry about missing your chance to download Windows 10 on July 29, because you can always join the Windows Insider program, this will allow you to download a preview copy of the operating system.
Before you install windows 10
Processor : 1GHz or faster with support for PAE, NX, and SSE2
RAM : 1GB (32-bit) or 2GB (64-bit)
Hard disk space : 16GB
Graphics card : Microsoft DirectX 9 graphics device with WDDM driver
If you want to take a peek at Windows 10, you can install the tech preview
Download Windows 10 Insider Preview and install on virtual machine to take a look at what its like to use.