Open your iTunes library. Click on and select the song you want to make an iPhone ringtone. Right-click on the song. Select “Get Info” from the menu that pops up.
Select “Options” from the top of the information window. Play the song and select up to 40 seconds of the song you’d like to be the ringtone. Enter that segment in the Start Time and Stop Time fields. Click “OK” to save.
Now you must create an AAC version of your edited song. Click “Advanced” then “Create AAC Version.” This should create a file below the original that looks identical but has a different time figure (under :40) that reflects the cut down version of the song.
Click “File,” “Show in Windows Explorer” in iTunes. Right-click on the file and choose “Rename” from the appearing menu. In the extension portion, which reads “.m4a,” type “.m4r” instead.
Keep the Windows Explorer folder open but return to iTunes. Reselect the shortened AAC file if it is not already selected and choose “Edit,” “Delete” from the menu bar. Choose “Remove” from the appearing dialog box. Click “Keep File” in the next dialog box. This allows you to reimport the file as a ringtone instead of a music file.
Bring up the Windows Explorer window again. Click and drag the .m4r file to the iTunes window. Release the mouse and locate the file in the Ringtones library panel at the left of the application.
Connect your iPhone and drag the ringtone from the Ringtones library to the “Devices” icon in the source panel. After a short syncing period, iTunes alerts you that you may disconnect the iPhone. The ringtone is available for you to use on your phone.