There are many software to resolve the problem,such as Xilisoft WMA MP3 Converter ,ImTOO WMA MP3 Converter, MP4converter MP4 to MP3 Converter and ect.
So i take MelodyCan converter for example. It supports converter WMA to MP3, MP4 to MP3. Besides,it supports converter to MP3 from almost audio files.To our joy,it has fast speed and is easy to handle. Why not to download free trial version to have a try.
Hope it`ll help smb 8)