I have recently came to know the upgrade of Android Jelly Bean to Kit Kat OS. Different brand smartphone have different types of option to upgrade compatible OS.
For Sony smartphone, there is option that 'Sony Xperia PR handle' from that you can upgrade from Android Jelly Bean to Kit Kat.
For Motorola smartphone, there is a page called 'Your Home for Upgrades' from there you can upgrade from Android Jelly Bean to Kit Kat.
As of now, Samsung and LG have not given this internal option directly to upgrade latest OS except external upgrade method.