The original frigate skin appeared to me to be more of a corvette (16 gun ports with 2 or 4 theoretical guns on the quarterdeck). The new skin now boasts 26 gun ports. Combined with a theoretical 6 guns on the quarterdeck, the frigate now belongs to a true frigate class, rather than corvette.
Goes into your Mod(or root)/Assests/Art/Units/frigate folder
Goes into your Mod(or root)/Assests/Art/Units/frigate folder