I thing you can flash any version of the firmware using the flashtool the is 3 check box on the right top corner to flash without wiping the data..
..... I would advise do not
install kitkat on top of the 4.3 without wiping data..
Don't rush, it is not that great, clam down.
4.4 is laggy, sound is shuttering and sd issue is really annoing, and there is no root so you will not be able to fix it..
. battery is .... ****ed up
Honestly you will regret...