Help with texture modding?

Hi people,

I`m new to modding myself, but what i want to do is edit Lucas` face texture so that he has stubble/a beard.

i used the oaf extractor and i think i found his head texture (was hard to find without a search option and no clear file name) 

i painted some test stubble along his jawline and saved it as a .dds file.

now im stuck. where do i put the modded file?

thanks in advance