With iTunes, you can create ringtones from songs in your library by converting any audio file to AAC format and changing its extension from “M4A” to “M4R.” By default, you can drag files from your desktop to iTunes -- but not to a connected iPhone -- and M4R files are hidden until you select the Tones tab.
Choosing the Right Settings
To enable dragging files from your desktop to iTunes, select “Manually Manage Music and Videos” in the iTunes Summary section. Connect your device to your computer using the included USB cable and press “Ctrl-S” to display the sidebar. Select your device in the sidebar and choose the “Summary” tab. In the Options section, select “Manually Manage Music and Videos.” With this option enabled, you can drag compatible files from your desktop directly to your device in iTunes.
Displaying Ringtones in Your Library
Open the iTunes Preferences window to confirm that ringtones are displayed in your library. Press “Ctrl-,” to open the Preferences window, select the “General” tab and enable the “Tones” option. After enabling this option, ringtones you drag from your desktop to iTunes are displayed in your library and automatically added to your iPhone when it is connected. Set a ringtone for your phone by choosing the “Tones” tab and selecting a ringtone from the menu.