How do i reopen a reconciled period to adjust an entry therein?

Hey raymond2, 

You cannot change the transaction type so to correct this you will need to delete the transfer and create the sales receipt manually. 

To delete, open the transfer and go to More > Delete on the toolbar, a warning message will appear that this has been reconciled - select ok to delete. The beginning balance of your reconciliation will now be out by this amount.

To correct, enter the sales receipt with the correct date, amount, and payment information, then reconcile this by going to the Cog Wheel > Reconcile, select the bank account, and enter the ending balance and ending date as of the last reconciliation. The transaction will appear to be reconciled, select this and then finish and save the reconciliaiton.

Thanks