Press space, and the item on the top is the save menu. Middle quits to menu, and I think the one on the bottom returns you to the game.
If you mean which file in the folder is the save file, then I just went ahead and checked, and they're as follows:
data0.dat is the saved config settings
data1.dat is the saved file for game progress (so basically "the" save file)
Not sure what data2.dat is, since it kept progress, but I imagine it's something like the blue gem count. It loaded my location fine without it.
Sorry I can't help with uploading mine, I'm somewhere on world 3 so I've already beaten the first two bosses.