First, open up iTunes in order to make a ringtone using iTunes. Find the song you want to turn into a ringtone by browsing through your music library.
Next, find exactly what part of the song you want to make a ringtone using iTunes. For example, if you want to use a specific section of the song from 21 seconds to 40 seconds, make a note of where you want the ringtone to begin and end.
Now, right click on the song you want to turn into a ringtone. Click "Get Info". Now, in order to make a ringtone using iTunes, click the "Options" tab.
Check the "Start Time" check box. Type in the point in the song where you want the ringtone to start in the format "minute:seconds" (e.g. the second mark would be 0:20). You can also be more precise by adding a period and putting milliseconds in after that (e.g. 0:20.150, would be 20.150 seconds). Also, click the "Stop Time" check box and enter where you would like the ring tone to end. Keep in mind ringtones can only be around 39 seconds maximum. Press "Ok". We are almost done making a ringtone in iTunes
Now, right click on the same song. Select "Convert AAC Version". If it is in another file format, you can go to "Edit" then "Preferences" and under the "General" tab click "Import Settings"; change the file format to AAC. After you select "Convert AAC Version" a new file will be created, but it will only be the segment of the song that you specified earlier.
Now, you have to find the file you just created. Right click on the new, shorter song and select "Open in Windows Explorer". The file extension should be .m4a. Rename the extension to .m4r by right clicking the file and selecting "Rename".
Now you can delete the shortened version of the song in your iTunes library. Then, double click the .m4r file and it will loaded into your iTunes Ringtone list. Now you can make a ringtone using iTunes!