How to change movie extension?

I editted a movie from my digital camera using microsoft movie maker however when I go to save it it only allows me to save it under the extension "movie maker projects" or "all files" however, all files doesn't work and I tried to use the movie maker projects but its not facebook compatible, so is there a way that I can change the extension so that I can upload the movie to my family on facebook? Thankss. :)