i tried several transcoding apps but the best way to convert audio is AUDACITY! It works on Windows/Mac/Linux Platforms.
install the one and only Audacity-Audioeditor (Freeware!) on your computer (ver. 1.3.x recommended for transcoding) from the website:
http://www.audacity.de or http://www.audacityteam.org
download the FFmpeg tool from the audacityteam.org website:
http://manual.audacityteam.org/index.php?title=FAQ:Installation_and_Plug-Ins#installffmpeg and install it.
start Audacity and tell the program where you installed the FFmpeg tools. in Audacity versions 1.3.x the mp3 export is already enabled.
simply drag and drop / open the wma file in Audacity. now you can edit/cut/... the file and export it to any common or uncommon audioformat!