Please Help?! Windows Movie Maker?

I made a movie with Windows Movie Maker and I want to upload it on this one site but it only allows files ending with this: .mov, .wav, .mp4, .avi, .wmv, but mine ends with .MSWMM. How can I change it? I know it works with Windows Movie Maker because some other people uploaded movies they made with it. How can I change it?