Note: Remember, trying out an early build like this can be risky. So it's recommended that you don't install the preview on your primary home or business PC. Unexpected PC crashes could damage or even delete your files, so you should back up everything.Steps to follow:
>> Downloaded a Windows Insider Programvfrom Microsoft to prepare your Windows 7 or Windows 8 operating system for the upgrade.
(It requires a restart of the PC so that the changes it made take effect. The device will boot into the current operating system after restart.)>> Open Windows Update console on your PC.
>> Click on the check for updates button. It may take a while for the check to complete. Initiate the Windows 10 update from install button.
Important notes:
>
Create a backup of your important files and data
before you proceed with the update.
> If you are running a 32-bit version of Windows, you cannot upgrade to 64-bit versions of Windows 10.
ref.