Here are the summarized technical details about the update addressed by Samsung and AT&T:
Effective July 9, 2015, AT&T will release a sofware update for the Samsung Galaxy S 6 (G920A). This update will be made available to customers via Firmware Over The Air (FOTA). A Wi-Fi connection is required for the update.
Software update includes
- Find My Mobile and Reactivation Lock enhancements
- Android OS security enhancements
- Android version: 5.0.2
- Baseband version: G920AUCU2AOF3
- Kernel version: 3.10.61-4823236
- Build number: LRX22G.G920AUCU2AOF3
The update files size is around 146MB,and it is now live via Over-The-Air OTA update. You can now manually check the update by hitting your device Settings>About device>Software update>Check for update. Just make sure phone hasn't been rooted nor modified so you can get the update without any hiccups. Noting that accepting a OTA updates on a rooted device will breaks its root and if you are not lucky enough it may also results into undesirable soft-bricks.
Source: AT&T support, Samsung support