Follow these steps to download Insider Preview:
Sign up for the Windows Insider Program, if you haven't already.
Read the system requirements.
Click one of the Download links on this page to download a special file—it's called an ISO file—that you can use to install the preview.
When the download is complete, transfer the ISO file to installation media such as a USB flash drive or DVD.
Boot your PC from the installation media, and then follow the steps to perform a clean install.
Windows Insider Preview Activation
You will need to install the Windows 10 Insider Preview build on a device that has been previously activated with Windows 10
or with a Windows 10 product key. For more details please see the article: Activation in Windows 10.
You'll need a third-party program to convert the ISO file into installable media—DVD burning software often includes this capability.
Remember, trying out an early build like this can be risky. That's why we recommend 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.
If you want to stop using Windows 10 Insider Preview and return to your previous version of Windows, you'll need to reinstall your previous version from the recovery or installation media that came with your PC—typically a DVD. If you don't have recovery media, you might be able to create recovery media from a recovery partition on your PC using software provided by your PC manufacturer. You'll need to do this before you upgrade. Check the support section of your PC manufacturer's website for more info.
After you install Windows 10 Insider Preview, you won’t be able to use the recovery partition on your PC to go back to your previous version of Windows.