So the short answer is if you have something like VLC Player or something that can play .ogg files, you can find the background music by opening the game folder, then open the "www" folder, to "audio", to "bgm". If it has a long wordy title, it's probably one of the game songs. If it doesn't then it's one of the engine's base asset songs. The difference in sound will make it pretty obvious.
So why that's how I'm saying to do it is because the songs were originally from a pack of like 200 free midis that Karugamo BGM put out, that I then ran through some edits and processing. Legally I can use the songs but I can't redistribute them. So putting them on Youtube is a bit of a grey area, and distributing them through other sites and stuff is definitely a no-go.