There are 2 ways this could be done - it comes down to how you work and how many payments you need to change.
Option 1 - Change individual payments
If you need to change one or two individual payments, when viewing the payment details you will see the name of the bank account in the top right, with a little pencil icon:
Clicking this will give you the option to change the bank account.
Option 2 - Bulk change the transactions
This is likely to the easier and quicker option which involves bulk moving the transactions from one bank account to another.
Firstly, go to Reports >> Chart Of Accounts, and scroll down to Assets and Liabilities. Expand this section and find the wrong bank account and go into it.
Tick the payments you want to move and then select the Move to new code button:
Select the correct bank account, and job done!
Hope that helps