Default Official firmware whitout Knox

Gals sorry if this was asked before, really sorry... i dont want to bother you..

I have some issues whit TWRP, the backup that i made of my official firmware (4.2.2 whitout knox) doesnt work.
The problem is that i installed a custom and now i dont know how to go back.

I know that in sammobile i can find the official 4.2.2 but ¿there is any way to install a 4.3 o 4.4.2 (oficial whitout knox)?

My head hurts.. after reading and reading i dont know what to do... i cant understand the modems and baseband things...

Cheers for the help