It looks like T-Mobile subscribers that own the Samsung Galaxy S4 are successfully updating to Android 4.4.2 KitKat. If you haven't received a prompt, you should do a manual check from the phone's Settings menu.
The update is about 388MB in size. Some users complain of slow download speeds over Wi-Fi. If the wireless route doesn't work for you, give Samsung Kies a try.
Updating to Android 4.4.2 will bring improved stability, a new camera shortcut on the lock screen, and an improved on-screen keyboard in addition to KitKat itself.
source: T-Mobile News