Lumia Cyan will bring an updated Creative Studio app, support for the low powered Bluetooth 4.0 LE, and slider controls that will help Windows Phone users customize the brightness on their phone's screen. Those are just some of the features that the update will bring to Lumia handsets.
Windows Phone 8.1 is being pushed out to all Windows Phone 8 models, and the Lumia Cyan update should be sent out globally during the summer.
Lumia owners in Thailand are beginning to receive Lumia Cyan update
1. Lumia Cyan update rolls out in Thailand
2. Update include customized brightness sliders