Hello,
With Images, many depend what version you use. if that last version, you may for one vehicle do export, and check XML file and folder with images:
{your site}/components/com_vehiclemanager/photos/
so you need only update XML file and move your main photos to that folder.
In you have version before, you will need check and rebuild image upload algorithm, because in before versions we create small images at time images upload
Thanks,
OrdaSoft team