You can use vlc
http://www.videolan.org/vlc/
The instructions:
1. Open VLC and browse to file.
2. Start playing - then press Stop.
3. File - Wizard
4. It will give you a pop-up �Streaming/Transcoding Wizard�.
Select Transcode/Save to file and Click Next.
5. Select Existing PlayList Item, highlight the .flv and click Next
6. In the next screen, Select Transcode Video and from the drop down box choose WMV3 (this has highest quality, though the output of the file may differ as per the original .flv file)
7. Select Transcode Audio and from the drop down box choose MP3 (for the quality to be higher, leave it at the default bitrate of 192) and click Next.
8. choose �ASF� as the �Encapsulation Format� and click Next.
9. You will be asked to select the file to save to, click �Choose� and browse to the folder where you want your new file to be saved.
10: !!!Important!!! Type in the file name in the �File� field with the extension of .WMV (example, lytebyte.wmv)
11. Click Finish.