Bapi for Sales Order (VA02) change

hi frnds,

i need to update one field of Sales order item. i feel BAPI_SALESORDER_CHANGE is right bapi for doing this. can u tell me step by step procedure for this. remember this is my first bapi. first i thought to do in BDC and i feel Bapi is good than BDC. i thought to do it in Bapi.

i am expecting your valuable help for doing this.

Regards,

Balu