To add a ringtone on your computer to your phone:
1. Find the file in your downloads folder and open it or drag it to itunes.
2. Look in the "tones" section of itunes and drag the desired ringtone to your iphone.
3. In your iphone open "settings" then go to "sounds" then go down to ringtone and select the new ringtone you added to the list.
Voila!