Update summary
Effective June 23, 2016, Microsoft and AT&T released a new Windows 10 update for the Nokia Lumia 1520. To download the update, you must download and install the Windows 10 Upgrade Advisor app from the Windows app store. The update will be available for download via Firmware Over The Air (FOTA). A Wi-Fi connection is required for the update.

Software update includes
  • Windows 10 operating system
  • Built-in Applications photos, maps, messaging, music, video and more.
  • Cortana personal assistant
  • Improved multi-task and organize capability for improved productivity
  • OneDrive - online storage
  • Secureboot supports quick and secure reboot
  • Windows Defender - malicious malware protection
  • Windows Store for access to hundreds of thousands of applications.

Source: Update the software of the Nokia Lumia 1520