1. To Allow the user to Modify or Delete Previous dated Sales Bill, Enable the configuration that is shown below for the particular user.
Click Tools--Options--Options--Billing
2. To list the batch stock details in Sales bill based on FIFO or Short expiry, the option has to be selected whichever is required as shown below.
Click Tools--Options--Options--Sales--Item Wise Option--Near the Stock Flow as shown below, press F2 to list the options to select as shown in the right bottom.