We think that the most simple freeware video-converter is Aicoosoft Video Converter. It allows you to convert Flash FLV video in AVI/MPEG/WMV and also to change options of quality of video and audio, as well as converting several video reels at once.
Download the converter from an official site: Aicoosoft Video Converter
Install and start it.
Press the button "Add" and add initial *.flv video.
Press the button "Settings" and choose a format in which you want to convert ("output format") and press Enter.
Choose a folder where the program will save converted video ("output directory") and press "Convert".