Changing an invoice from paid to unpaid

I have an invoice that is marked as paid but I need to change it to unpaid. How I do I change it back without deleting it?

To change an invoice from being paid to unpaid, please proceed as follows:

Step 1

• Click on the Debtors toolbar option
• Click on the Invoices tab
• Select the Invoice that you wish to change
• Click on the Edit button

Step 2 

In the payment details box :

• Clear out the Date Paid. Place the cursor at the beginning of the date and press the Delete key on your keyboard
• Clear out the Amt. Paid
• Click on the OK button

This will delete the payment details and revert the invoice back to unpaid.