NOTE: Special Thanks to Paul Thurrott for being the willing guinea pig.
If you haven’t heard already you’ll have to go though a few steps to get it. It turns out that *ALL* 1520s have Bitlocker already turned on and there is no way to turn it off. Which means that you’ll have to downgrade your phone back to Windows Phone 8.0 using the Nokia Software Recovery Tool. That *WILL* replace the firmware and wipe out all your data. Hopefully you’ve previously had Backup turned on and your stuff is in the cloud.
During the process I hit a snag when the Recovery tool wasn’t able to reconnect to my phone after successfully downgrading it… so I wasn’t immediately able to reconnect properly to any of my backups. TO BE CLEAR: If I had been able to reconnect my phone to my Wi-Fi and log into my Microsoft account BEFORE the timer on the Recovery Tool had ended I would have been able to restore my phone. So the “problem” above was entirely due to user fumbling… and it would’ve been nice if Nokia had given me a bit more time on the timer. ;/
I decided to try a hard reset (since I didn’t have anything to lose anyway) and *duh-duh-duh-dah!* there were my available backups. It took about 20 minutes to do the restore but it worked… with the exception that I had to re-enter nearly all my email account passwords (and I have a LOT with extra-strong passwords).
It appears that many of my personalized settings (lockscreen, theme, glance, etc.) weren’t restored but I don’t really consider that to be a problem.
Long story short — (so far) I’m happy with the result despite the bumps and bruises. 😉
Here are the instructions for how to successfully downgrade from the Develop Preview then upgrade your phone to Lumia Cyan: http://winsupersite.com/windows-phone/att-rolls-out-windows-phone-81-nokia-lumia-1520
If you need to hard reset your 1520, here’s how to do that: https://www.youtube.com/watch?v=aqJyEMmQJ6g