To delete the invoice and recover the Delivery Order and enable editing, please follow the instructions below:
Delete invoice:
Open Administration, Administrative Tools, Tools 2, and select Change to InvNo.
Look for the Delivery Order number and delete To Invoice.
Apply.
Open Customer & Sales, Sales Invoices, and Search Invoice, and delete the invoice.
Open Customer & Sales, Delivery Order, and edit the bill.
Alternative: Change Setup
Open Administration, Administrative Tools.
Select Allow Edit Quantity of Invoice generated from DO.
Ok.
You may now edit the Invoice and related Delivery Order.