If you have the orig. cd it would be better to just re rip it. Transcoding wma to mp3 would only make them sound worse .You'll get a lot more clipping , artifacts, etc , but If you still want to http://www.dbpoweramp.com/dmc.htm
is pretty good.
'What makes a good man go neutral? Lust for gold? Power? Or were you just born with a heart full of neutrality?' -Zapp Brannigan