There are times that you need to reset or change the starting number for orders, invoices, shipments, quotes or credit memos.
A simple way to do this is to go into phpmyadmin (or similar tool) and edit the eav_entity_store table:
LIMIT 0 , 30
4 = order
18 = invoice
24 = shipment
28 = credit memo
11 = quote
Simply enter the new starting number for any of the above types.
CAUTION: Make sure you don’t enter a starting number that is lower than any number already used or unpredictable results and issues can occur.