how do i convert my itunes to wav format

Select Edit > Preferences > General, click on Import Settings... then select WAV encoder from the "Import Using" dropdown. Then select the songs to be converted, right-click and select Create WAV version*.

Note, however, that unless you have a very specific reason to do so there's no benefit in converting to WAV format (especially if the original media files are in a lossy format such as MP3 or AAC). You'll get much larger files with no improvement in audio quality, and WAV files lack the ability to embed any metadata including artwork images.

* since you're on Vista and therefore using iTunes 12.1.3 or earlier, this function is available through the right-click context menu. The current version of iTunes (12.4) has moved this to the File menu.