If you are registered with App Studio (anyone can) OR a registered Windows Phone developer, then you can receive pre-release OS updates on their dev phone, directly from Microsoft. You can use the Preview for Developers
app to opt-in your phone to receive early Windows Phone updates before they are generally available, enabling you to run and test your app on real hardware running the latest OS before your customers.
This tutorial will show you how to register and to download and install the Preview for Developers
app to be able to receive pre-release OS updates
on your Windows Phone 8 and 8.1