If you are using the abstraction APIs, just remove the line item from the IShipment.LineItems (then call IOrderRepository.Save to save the order)
If you are still using the concrete implementations, take a look at PurchaseOrderManager.RemoveLineItemFromOrder(OrderGroup, lineItemId), then use order.AcceptChanges to save the changes
Thanks for your information , i will look into it .
We are trying to remove line items which are already present in the purchase order. Basically we wanted to change the product code in the line items of the purchase order. Is there any specific way to remove that information?