BAPI/FM to update Proof of Delivery Status

Hello Experts  ,

     I want to change the Status of proof of delivery from 'A' to C' i.e Not Relevant to Confirmed State , for the deliveries which were completed. So Do we have any standard BAPI which satisfies my requirement or Do i have to write any Custom Function Module to update the status. I tried with "WS_DELIVERY_UPDATE_2" function module to update the status but i didn't get it done. If it is the right one , let me know what parameters i need to pass to get the status updated. Could anyone help me in resolving this.

Thanks,

Uday.