AT&T has begun rolling out Windows Phone 8.1 update to all Nokia Lumia 1520 devices, bringing a slew of new features including Cortana.

Nokia Lumia 1520 users on AT&T's network are getting lucky this week. The second largest wireless carrier in the United States started rolling out the most awaited Windows Phone 8.1 update to Lumia 1520 users adding a host of new features to Microsoft's mobile operating system. The update is a major improvement from the original WP8 version as it brings virtual assistant Cortana among other features.

According to AT&T's official blog, Lumia 1520 devices on its network will receive the Windows Phone 8.1 or Lumia Cyan update starting 1 p.m. ET, Thursday. The carrier noted that the devices will unlock the ability to personalize the Start Screen with customizable Live Tiles, enhanced camera features, new Action Center and more.

With Cortana being the centerpiece of the update, AT&T said Microsoft's first virtual assistant stands out in the crowd with its unique features that can set reminders by people and by time or location. "She can remind you to thank your mom for sending that care package of cookies in the mail the next time she calls to check in on you," the carrier wrote in its blog,Thursday.

AT&T also highlighted other features that will be added to the smartphone after the update. Lumia 1520 users will be able to customize Live Tiles on the Start Screen by changing the size and color and also pin new apps, music and people to the main screen. Even the Lumia 1520's 20-megapixel PureView sensor gets better with the update with new features and apps for sharing images.

"The Windows Phone 8.1 update also takes full advantage of the Lumia 1520's Quad-core processor, large, bright 6-inch HD 1080p display, and Nokia Rich Recording suite - four digital microphones and 140 dB recording range provide unparalleled stereo sound for video captured by the Lumia 1520," AT&T added.

The update also rejuvenates OneDrive, Skype, Office and Bing for a more connected experience while on-the-go. With a new Action Center, users can easily manage notifications and quick actions. The Cyan update makes typing easy with new Word Flow keyboard that requires users to swipe the finger across the letter to form a word, a feature that has long been seen in other Android devices and is coming to iOS in the next update.

How to install the update?

In order to update the Lumia 1520 smartphone on AT&T's network, users must ensure the battery is at least 50 percent. Navigate to Settings Live Tile > Phone Update and download and install the update. Restart the phone when prompted and the update is completed. The update weighs about 250 MB and requires secure and a stable Wi-Fi connection.

Lumia 1520 owners who tweaked their phones with Preview for Developers must downgrade the OS before getting Cyan, Paul Thurrott's Supersite for Windows reported.