According to Sony Official Changelog Changes are
This upgrade for your Xperia™ smartphone includes many improvements, such as:
- Google Android 4.3 (Jellybean), bringing smooth UI and graphics enhancements
- New version of Battery STAMINA Mode for longer battery life
- Updated camera interface bringing Burst Mode, Superior Auto & More
- Updated applications from Sony featuring Walkman, Album, Movies & More
- Latest security enhancements from Android 4.3
New firmware is already available through OTA or Sony PC Companion.
OTA can be done by going to Settings > About phone > Software updates > System updates.