There is no official change-log available but as per folks at SamMobile, the update brings the following changes.
- OpenGL 3.0 Support
- Galaxy Gear Support
- TRIM Support
- ANT+ Support
- Samsung KNOX Implementation
- Pre-loaded Samsung Wallet
- Improved RAM management
- Improved Display colour reproduction (Display looks much sharper than before)
- Improved TouchWiz Launcher (Much less launcher redraws and less lag)
- New Samsung Keyboard, Samsung Browser, Reading Mode
- New Camera firmware
- Minor UI tweaks
To manually check for the OTA update on your Galaxy S4, go to Settings > More > About Device > Software update > Update.

One reply on “Samsung begins Android 4.3 update roll-out for Galaxy S4 I9505”
Waiting for I9500 update in India