I recently had to convert a bunch of .wma files into .mp3 files for a teacher to allow her students to listen to the files on their MacBook Pros. The only challenge was the pace of the audio files was a little slow and she wanted her students to have the option of speeding up the audio.
The first hurdle, converting from .wma to .mp3 was fairly easy. Cloud Convert is an excellent free site that allows you to convert most types of media files effortlessly. Just upload your file and choose the type of file you want to convert it to.
Once she posted her files to our PowerSchool LMS students were able to download the files and play them in VLC (a free media player). VLC has a feature under Playback to choose the speed at which you would like your audio file to play. Moving the slider adjusts the speed slower or faster depending on your preference.