2. Scroll down and click Phone->Click Get the preview.
3. Download the Windows Insider app on your Windows Phone device. Now open the app and sign in using your Microsoft account. After signing-in Click on Get preview builds.
4. Here you'll have to choose between receiving OS updates. Tap Insider Fast to stay on the bleeding edge or pick Insider Slow if you'd like a slightly more reliable build. Take a look at all the warnings and then Click Accept.
5. Tap the Windows button on your phone->Go to Settings > Phone Update->Click Check for updates.
Congratulations, Now you will be able to download the latest Windows 10 builds for your Smartphone.