You can download the update via Firmware Over the Air (FOTA).
You must connect your device to Wi-Fi to download the update.
Although there should be no impacts to settings or data, we recommend that you back up your media files to an SD card, a PC, or using a favorite application, prior to upgrading the software.
Update & verify software
Update software
Make sure your device is fully charged and connected to Wi-Fi.
Swipe down from the Notification bar, then tap the Settings icon.
Scroll to and tap AT&T Software Update.
Tap Check for Updates.
Follow the on-screen prompts to download and install the update.
The device automatically restarts once the new software successfully installs.
Verify software update
Swipe down from the Notification bar, then tap the Settings icon.
Scroll to and tap About phone.
The device has the latest software if the Android version, Baseband version, and Build number match the current update details.