Hi DurgaPrasad,
Now inbound delivery datasource, if you need on one table i.e. either header or item, you can make it delta enabled using changed on date available in the table. ( which table user want is based on the requirement, you can get it clarified from user if they are looking for header information or item information)
If consider requirement is to bring data from both tables then you need delta based on two changed on dates one is from header table and another is from item table, to built this you need to go for a Function module based generic datasource. Below link show how you can do this.
Also one addition to this is you can built a view and then instead writing complete extraction logic you can use view to bring delta (only extraction logic change to the logic mentioned in below document)
I guess this will clarify your doubts.
Regards,
Ganesh