We'll do a little trick to create a WMA to MP3 "converter" for you to ease your conversion.
First of all, download FFMpeg. It's free, and you can get it here.
1) If your files are in one directory, you can write in batch file:
FOR %I IN (*.wma) DO <path to ffmpeg.exe> -i "%I" "%I.mp3" ren *.wma.mp3 ????????????????????????????????????????.mp3 delete *.wma
Now copy that batch file to directory where are placed your WMA files and run it.
2) If you want to select them and convert manually (with drag'n'drop), then write in the batch file:
ffmpeg -i %1 -ab 32 %1.mp3 ren *.wma.mp3 ????????????????????????????????????????.mp3 delete %1
Now your "converter" is ready. Drag and drop your files on it to convert files.