How to use FM to update the standard table LIPS?

Hi, I am newbie on the SAP ABAP.
It is not recommended to use insert, update, modify to modify the standard table,

If I want to use FM 'WS_DELIVERY_UPDATE' to update one of the field in table LIPS, can have explanation on how to call the function? Means what should be import and what should be export, a bit confusing on it.

The following is the action that I need to be proceed:

UPDATE LIPS SET LFIMG = LT_BCODE_I-MENGE
              WHERE VGBEL = LT_BCODE_I-VGBEL
              AND VGPOS = LT_BCODE_I-VGPOS.