To set your iPhone ringtone, do the following:
1. From the home screen, tap the Settings icon.
2. In Settings, tap the Sounds menu.
3. In Sounds, tap the Ringtone menu.
4. This menu shows you the list of all the ringtones available on your iPhone. If you tap one, it will play, allowing you to preview the ringtone your iPhone will play ever time a call comes in.
5. When you have found an iPhone ringtone that you like, tap it to select it. A checkmark will appear to the right to indicate that it is selected.
6. Now, whenever a call comes in, that ringtone will play. Just remember to listen for that sound, and not a ringing phone, so you don�t miss any calls.
If you want more help check out this link:
https://www.youtube.com/watch?v=bf65uChjlfM