You will need to downgrade from WP8.1 Developer Preview to Windows Phone 8 using Nokia Software Recovery Tool prior to updating to Cyan.
Windows Phone 8.1 Preview users still need to downgrade their OS in order to get Lumia Cyan | Windows Phone Central
I'd rather play the patience game and wait for the rollout of Cyan for DP users. Microsoft has fixed the Bitlocker issue in the meantime and now it's only a matter of time, until all devices running DP receive the firmware. Okay, time AND carriers.Anyways, I definitely prefer waiting for the update instead of flashing my device, hence losing my precious data.
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I had nothing to lose, since I have all my pictures/documents in OneDrive, and I don't have any music stored locally.