To modify a transaction just click Bank > View/Add Transactions button > Click on a transaction > Change any details > Click Update. If you select a payment that is associated to an invoice or a purchase you will be taken to that screen where you can amend the details. Selecting a bank transaction will take you to the screen shown below. Please be aware that changing a transaction that has been previously reconciled will cause that and subsequent reconciliations to be incorrect, you will have to re-reconcile all reconciliations thereafter.