Editing recurring payments
Changing payments - users
Users can do this themselves through the app if it is enabled (per payment group) under Settings > Advanced Settings > Registration Settings > Allow changes to registrations after completion.
In the app under Me > My Account > Finance they can click on the fund name to see details and an Edit Registration link will be shown:
If you haven't enabled editing after completion then the "Cancel Registration" link is still available and so the user could cancel it and create a new one.
If you have enabled registrations to be edited, and you also require approval after a registration is edited, then you would probably benefit from setting up a notification under the 'Jobs' section for that group.
Changing payments - Admins
Admins can always edit a registration through the web office by opening up the registration window and clicking Tasks > Edit this donation/registration. This includes admin options for overriding fixed amounts, switching to offline payments and supressing future emails.
If you are DELETING a recurring payment please see this article for instructions.