Hi Eva,
2 things. One, you can edit the due date of an AR transaction by enabled a Company Profile option 'Allow edit of due date'. With this option, when you edit a customer and look at their transactions, the Due Date will become editable.
However, the other part is that you cannot edit a due date to be before the invoice date. Edited due dates must be equal to or later than the invoice date.
Because the transactions have future dates, they can only be cleared to history by running period end or printing statements with a date after these future-dated documents. If you are OK with doing this (you would need to re-run the function with today's date to reset, and essentially all completed transactions will get cleared), then first make a backup of the AR data (just in case) and then go ahead.
Otherwise, you can hide these documents from printing on statements by only choosing to print Outstanding Transactions Only, and keep them around until the date comes.
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Regards,
Softrak Tech Support