how to change wma into mp3?
 

i installed xmms, i'm not sure if i must install other plugins for changing wma into mp3,if so,which plugins?

There's an input plugin listed here for reading wma files: http://xmms.org/plugins.php?details=3
For outputting to mp3 files, here: http://xmms.org/plugins.php?details=140
Otherwise, just go to xmms.org and look through the plugin lists.