If you already own a copy of Minecraft for PC or Mac, you’re eligible for a free copy of Minecraft: Windows 10 Edition Beta.
To download your copy, first log into your Mojang account. Click the “Redeem” button on your account page, sign into your Microsoft account, and follow the instructions that follow.
That’s all you have to do get your free copy of Minecraft: Windows 10 Edition Beta. Go to Mojang for further details.