Doh! Sorry about that.
In that case do what HaxO said (turn on double sided geometry), but also open up the material applied to it and check “Two Sided” as well, build/save the material, and you should then get an image on both sides.
Hope that is more helpful… Is double sided what you are looking for or just completely flipping it? If you want that (and rotating the mesh is not an option) you will need to edit the model in a 3d program unfortunately. 