Enter details of your Microsoft account and click on "Login".
Microsoft will ask if you allow a AppStudio have access to your information. Click "Yes".
Enter a username, your email address, check the box and click on "Register".Already a developer!
On your smartphone, go to the app store (icon of a bag with window for Windows) and search for "Preview for Developers". Click on "Install".
When installed, open the app. You'll have to sign in with your Microsoft account with which you just made developer.
Activate the "Enable Preview for Developers" box and click "done".
Go to Settings> Update your phone and check for updates.Windows Phone 8.1 have already waiting for you!