How to change android version Jellybean 4.2.2 to the newest update?
Accorrding to GSM ARENA your phone officially supports an upgrade to 4.4.2 Kitkat. However you can try a custom ROM for your phone. Read more about rooting and recoveries(Google is your friend)

As to why it is not updating to 4.4.3, maybe this will clear things out XDA-devs s4 zoom