There are probably several Sound Editing programs which you can use to convert the file format from WMA to WAV. The one I use is called GoldWave - a very versatile editor. You can download a trial version free from www.goldwave.com
Load the WMA format file and then save it in the new WAV format. However, converting a file from a compressed format such as WMA or MP3, to WAV format, will not restore the quality of the original WAV file, since some of the content of the original file is lost, during the compression process.
Having said this, the 'converted' WAV file should not sound any worse than the WMA file, from which it has been converted.

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Willum
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Willum

After silence, that which comes nearest to expressing the inexpressible is Music.
Aldous Huxley
( especially when the music is played on a KN7000....)