How do I change audio format?

A little while ago i was cleaning up files on my mothers computer, and I found some old music on there that i wanted back. So i put it on a thumb drive and transferred it to my mac. The problem is the files are .wma, and in order to get them into itunes they need to be a different file. i tried to change them to .mp3 which seemed to work but they wouldn't play sitll, nor would they drag into itunes. how do i convert the files?