how to change invoice and delivery order number in virtuemart

how to change invoice number and delivery number in virtuemart like this the starting invoice number will be 9546900001 & delivery order number will be DO953700001....... Invoice number 95469 will be fixed and only 00001 will increase, once reach 99999 will move to 100000.Delivery order number DO9537 will be fixed and only 00001 will increase. Please help me! Thks!