Hello Krishna,
Use the function module BAPI_SALESORDER_CHANGE,
CALL FUNCTION 'BAPI_SALESORDER_CHANGE'
EXPORTING
salesdocument = r_salesdocument
order_header_in = r_order_header_in
order_header_inx = r_order_header_inx
TABLES
return = itab_return.
Pass only the above parameters, as you need to update only in the header table VBAK.
r_order_header_inx - Specifyupdate flag in field UPDATEFLAG as 'U' (Change)
Make sure to use BAPI TRANSACTION COMMIT after calling this BAPI.
Read the documentation of the function module, it is specified over there.
Regards,
Thanga