How to set a custom ringtone without jailbreaking the IPHONE4S?

How to set ringtones for iphone4? Open itunes, select File in the menu bar-add files to the library, and select songs as ringtones. Click Open and the song will appear in the music library. Right-click the song, select Show Introduction, select options, and fill in the start time and stop time (within 40 seconds). Select Create ACC Version for files with the same file name but less than 40 seconds. Right-click the newly-created song, select "Display in windows Explorer", change the format of "m4a" to "m4r", and change "Yes" to ps in the pop-up window; if you can't see "m4a", select "Display in windows Explorer" in the menu bar. Check: Find Preferences in the Edit menu bar of itunes, open it in General-Sources, and put a check in front of Ringtone, on the first page. Then "OK" You can see the ringtone in the database. Turn on the ringtone, and you can see whether your file has been converted into a ringtone. Then turn on the iphone in the device, select the ringtone, check the item "Synchronize ringtones", select "All ringtones" or "Selected ringtones", and then select "Synchronize" to successfully synchronize ringtones. Custom options are above standard options.