Default [Q] s4 m919

About my mobile
number of model: SGH M919
android 4.4.2 Version
version of the baseband :: M919UVUFNB4
KERNEL VERSION: 3.4.0-540242
version number: KOT49H.M919UVUFNB4
operator: orange tunisia

hello all
* I received my new s4 but I switched it makes bug but not all the time plus I did not video call option
so I want to make a system for formatting elevate the existing rom and remove the t mobile demarage same applications and power istaller a new rom gt i9505 which is an international version that owns the video call
if you can tell me the steps to follow to do so and the software installed
* apologize my English if there are error
thank you to all