Edit default background [tesla game]

Hey there, I purchased tesla game about six months ago for a forums that I maintain. I've been asked by the owner to change the background, but I'm having trouble locating the file. Originally I thought I just needed to replace 1.jpg, but that only changed the picture in the background editor, then I found the bodybg.jpg file, so I replaced that too to no avail. I can't seem to find any other location where this image exists on my ftp server, but somehow it is still the background of the forums. I'm looking for a way to either edit the default background, or to force another picture on all users.

Thank you for your help Dr. Envira, I myself hope to become a radiologist one day