There are two types of manually recorded payments:
1. A payment from a buyer (made on Enter Receipt tab)
2. A payment to a Supplier (made on Record Payment to Supplier tab)
If you need to adjust the entry, you can do so by navigating to the Financials>>Review Payment History tab, then clicking "Update Payment Note" to the right of the entry you wish to edit.
2. You will be taken to the editing screen where you can make your changes. Be sure to click "Update Payment" to save your changes.