The firmware comes with model number R820UXXU1CTJ5/R820OXA1CTJ5 and is about 61MB in size.
The Voice Support can be turned on or off and it essentially helps during running and swimming by telling you whether to push harder or ease off. It analyzes your pulse, correlates it with pace and other data, and in theory should help for better training with less fatigue and time to recover.
The update also brings fixes to stability issues with the Bluetooth connectivity, minor bugs, and overall improvements for some features. The firmware is available in South Korea and should hit other devices soon.