Please double click the booking that was checked-in

In the Pricing bookmark you can change the total price of the reservation if it is necessary:

If the guest have already made the payment, however you would like to correct this data you should enter your Front Desk --> Accounts:

Find your transaction and double click on. 
You will see the Edit Transaction window, where you will be able to edit the amount of transaction. Please also correct the description of the transaction to highlight that it was edited.

Now when the amount of the transaction is correct you can also correct balance if it is necessary:
Please double click on the booking and enter the Change Balance option.
Insert the correct balance and the reason for a change. Accept the change by clicking Ok button.