Use the WAV encoder in iTunes.
iTunes: How to convert a song to a different file format - http://support.apple.com/kb/HT1550 - including information about different formats and discussion about compression.
In iTunes11: File > Create New Version
In iTunes 11 "Create..." is in the File menu, not the Advanced menu.
Why do you want to convert to WAV? It won't make the quality any better and WAV format doesn't store labels/tags so your song information will be lost except for what is in the file name.