The upcoming Windows 10 is now available for download, free. This is the Technical Preview version of Windows 10 which means this version is for developers or enthusiast and not for end users. To download Windows 10 Technical Preview ISO, you will need a microsoft account. You can follow these steps to get Windows 10 Technical Preview ISO file.
A. Sign up for Windows Insider Program
Go to this page and sign up for Windows Insider Program. You will need a Microsoft account to do this.
B. Download Windows 10 Technical Preview ISO
Once you log in to Windows Insider, navigate to http://windows.microsoft.com/en-id/windows/preview-iso to download the ISO. Scroll down on that page and find the following download section.
You can find many available languages on that page. Click the preferred language to continue. Next, select the version of Windows 10. You can choose either 64 or 32 bit version of Windows 10.