Here are the steps to convert a WAV file to MP3:

1. Open Windows Media Player on your computer.
2. Click on the "Organize" button and select "Options".
3. In the Options window, click on the "Rip Music" tab.
4. Under "Rip Settings", select "MP3" from the "Format" drop-down menu.
5. Click on "Apply" and then "OK".
6. Insert the WAV file you want to convert into Windows Media Player.
7. Click on the "Rip CD" button.
8. The WAV file will be converted to MP3 format and saved in your music library.

Alternatively, you can use online tools such as FreeConvert.com or Convertio to convert your files.