Can I change the file extension manually? Or do I have to get a special video editor or maybe converter for that? I am not such an advanced computer user, I have never faced such problems before, so I really don't know how to handle it, and any help will be very much appreciated.

Liz, May 2012

Hi, Liz,
You are welcome, and don't worry about having a little experience, you will gain it soon, a couple years ago I was only a beginner myself.
There is no way to do it manually, so a video converter is required. This is the one I use, very handy, smart and free for you to get:
http://convertflvtomp4.org

Hope that helped and good luck!

Sarah, May 2012