For payments to be deleted, they can not be marked as reconciled. In order for you to delete a payment that was previously marked as reconciled, you'll have to mark the payment as not reconciled first.
To delete your reconciled payment, follow the steps below:
1) Click "More", navigate to "Bank Accounts" and then click "Bank Reconciliation".
2) Click "Reconciled".
3) Find the payment you'd like to delete, and click "Not Reconciled".
4) Back in the "Not Reconciled" tab, find the payment and click the checkbox next to it.
5) Click the "Item selected" drop-down menu, and then click "Delete".
6) Click "Yes".
What happens now?
The payment has now been moved to your "Recycle Bin". It'll sit there for 30 days before being permanently deleted.