Where can I find free WMA Conversion Software?
If these are unprotected files (non-DRM), you should be able to drop them directly into iTunes on a Mac and convert them to MP3 or AAC. I've never owned or used a Windows PC so I don't know if the same thing will work on Windows iTunes, but you could give it a try.

On a Mac, you can also install Flip4Mac, which enables you to load WMA files in QuickTime and convert them to MP3 or AAC. If you have a bunch of files, you could set up an Autmomator action to automatically do this on a folder full of files.