Have a look in the Buildings & Units category.

DJ's original guide to editing unit textures:
https://forums.totalwar.org/vb/showthread.php?t=50469

A Beginner guide from Lentonius
https://forums.totalwar.org/vb/showthread.php?t=58962
But there's a lot of stuff about UV mapping there that, not being a modeller, I don't understand.