1. Open iTunes and select the song you want to edit.
2. Right-click on the song and select "Get Info".
3. In the "Get Info" window, click on the "Options" tab.
4. Under "Options", you will see the "Start Time" and "Stop Time" options.
5. Use the "Start Time" and "Stop Time" options to set the new start and end points of the song.
6. Click on the "OK" button to save your changes.
Please note that this will only change the starting and ending time of the song. For additional features, consider using audio editing software or apps specifically designed for editing and trimming audio recordings.