.rez filesize

Hey there,

I need some help over here. I downloaded this mod, made by Ali, but since it only changed the colors of the bodies, and not the head/face i decided to do that by myself. So i started changing textures and by the time i was done i noticed a huge difference in filesize.
My modified CHARS_T_FACE.rez was about 25mb while Ali's modified CHARS_T_BODY.rez was only 4mb. My question is, how do i get my rez files smaller? I suspect it's just a way of saving the .dtx files in photoshop, but i'm not sure. Please help

GreetZ, Basso