From your dashboard, click on "Billing" on the left-hand side then select "Invoices" from the drop-down.
From here, you will have two ways of editing the date of the invoice. Note you can use the filters at the top of the page to find the invoice you are searching for.
From this list view, click on the date under the "Date Due" column and manually edit the date. Note: you must click "Save" for each individual date you change.
Option 2 (Better for adjusting those on monthly payments):
Click the account ID # under the "Account ID" column next to the invoice you want to adjust. From this view, you will see all invoices associated to this player. Here you can adjust any date for any invoice you want to alter by clicking on the date. Note: you must click "Save" for each individual invoice you adjust.