On Wednesday, January 21, 2015 at 1:17:56 PM UTC-6, Moe DeLoughan wrote:
Want Windows 10? You got it: for free. This is a sea change in
Microsoft's strategy when it comes to upgrades. Gratis upgrades will
be available for Windows 7, 8.1 and even Windows Phone 8.1 users for a
full year.

http://gizmodo.com/windows-10-is-a-f...ear-1680771504

Here's "Windows 10 Technical Preview" ISO download with COA key.

http://windows.microsoft.com/zh-hk/windows/preview-iso