Open the iTunes software program on your computer. Install any updates that that the program asks you to install.
On a Windows computer, right-click on the song that you want to shorten and select "Get Info." On a Mac, hold down the "Control" button and click the mouse.
Locate and select the "Options" tab.
Enter the time in minutes and seconds that you want the song to stop and check the "Stop Time" box. Repeat the procedure if you want to shorten the song by starting it after its beginning and check the "Start Time" Box. Click "OK" to save changes.
Select the song by right-clicking it on a Windows computer or holding down the "Control" button and clicking the mouse on a Mac computer. Select the "Create MP3 Version" option to create a version of the track that will play at the desired length.