Nokia E72 - How do I change a ringing tone to a contact or contact group on my Nokia device?

In the Contacts application, open a contact or select a contact group, select Options > Ringing Tone (or Group > Ringing tone), select the one from the list of ringing tones. 

To remove the assigned ringing tone, select Options > Ringing Tone and Default tone from the list of ringing tones.