In the Finance section of a donor's profile, the Donations section lists every payment made by the donor. 

You can click Monthly plans and Installment plans to see those listed as well. To edit any donation, hover over it and click Edit. 

If you edit a monthly plan, you'll be taken to the Dashboard of this plan. At the bottom, you can see a list of all donations associated with this particular plan.

You can hover over and click Edit next to either of the previous donations to refund the payment that already occurred. Or you can go to the Settings area of the monthly plan to cancel future payments. 

All of this is happening within the People section of my control panel. If I go to the Finances section, I can review all donations made in my nation. Filtering the Finance section provides a great way to sort financial transactions. Additionally, Finances > More > Monthly plans lists all monthly donations, and Finances > More > Installment plans lists all installment plans.