Hi Fred, If you have bought the ring tone through i tunes then just plug your phone into the computer, (with the white lead thats part of your charger) then itunes should start automatically if not double click it to open it. Oncer i tunes starts just go to "file" in the top left hand corner and in the dropdown menu you will find the sync iphone button, click this and after a couple of minutes the ringtone will be on your phone! If not let me know cos there are other things that may need changing.
Hope this helps, let us know how you get on, Joel