Go to the mod’s data folder and find the VehicleSize text file. In the file find the Federation ships. Note the entries for the Primary Bitmap Name and Alternate Bitmap Name. The Primary Bitmap is used first. If the Primary Bitmap is not found, then the Alternate Bitmap is used.
Bitmap Name:
This is a bitmap name for the picture which represents this vehicle.
This is usually the same as the name but with no spaces. This name
is used as the very Last section of the full bitmap name.
A Vehicle Bitmap is normally named
[Empire Name]_[Portrait/Mini]_[Bitmap Name].bmp
The Empire Name is your empire name.
Portrait or Mini is the type of the picture. Portrait are 128x128 and
in an isometric view. Mini are the top-down 36x36 tiles used in space.