Everyone wants to personalize their ringtones in iPhones, but Apple does not make this process easy. However, keep in mind that even though customizing an iPhone's ringtone is not simple, it is possible. Unlike other phones that allows for personalized ringtones, Apple needs you to make use of a Mac before you can create a custom iPhone ringtone. Here's how you can make that happen:
Start by opening the sound file in your Mac through iTunes. Keep in mind that you will have to export another copy of that file and make its length 30 seconds or less. Edit the length with iTunes and then export, or you may also use a third party app to edit the length after exporting.
Next step is to locate that AAC version. When you find the file, copy it and paste it somewhere easy to find such as your desktop. You should then change its file extension to m4r from m4a. After which, drag the file to the Tones folder, which can be accessed by going to the Music folder and then the iTunes folder. Then, open the file by double clicking or by dragging it to iTunes. Once you navigate through Tones in iTunes, you should be able to see your desired iPhone ringtone in there.
In some cases when your iTunes can't recognize your iPhone ringtone file, it is probably because the original file was a non AAC file (probably it is an MP3 or WAV file). To fix this issue, delete the original and edited versions of the file from the iTunes. You may choose to keep the file in your device if you want to. Then move the original m4a file out of its default folder to another folder, preferably the desktop. Once done, drag the m4r file to the Tones folder by dragging it to iTunes or simply double clicking it. After this, the sound file should now be recognized by iTunes and it should now show up in the Tones section. You can now put the original version of the song back to their folders so they can go back to your music library.
Once you see the tone in the Tones section on iTunes, all you have to do is to sync the file in to your iPhone. To do this, you have to connect your iPhone to your Mac, and then press the upper left button to go to the device tab. After which, select the Tones section and check 'Sync Tones'. You may sync all tones or just some selected tones. After the syncing, your new iPhone ringtone will now show up on your handset.