Actually, it is fairly simple to do. First go to your weapon configuration files. Open up the desired weapon, search for "aim_hud_offset_pos_16x9". That will be the one for aiming. However, I do not remember how it goes "X, Y,Z, I can't remember" but test it. Now, that is for when you are aiming down the sights... Search for "hands_position_16x9", mess around with that one.