Here's one way you can convert the files.
Start by downloading and installing
VLC Media Player.
1. In the "Media" menu, select "Convert / Save..." (see "step 1.png").
2. In the window that comes up, click the "Add..." button and choose your first file, then click the "Convert / Save" button (see "step 2.png").
3. In the new window, enter a name for the WAV file in the "Destination file" box.
3a. The first time only, click the "Create a new profile" button. (see "step 3.png").
3b. Enter a profile name of "Audio - WAV", and create the profile as shown in "step 4.png" and step 5.png". You don't need to change anything on the "Video codec" or "Subtitles" tab.
3c. Click "Save".
4. Back in the "Convert" window, choose the "Audio - WAV" profile.
5. Click "Start"
6. Your file is now converted. Repeat these steps (other than 3a-3c) for each other file you want to convert.
If anything isn't clear, let me know.