Update does not working while select returns right results

I am trying to execute the query below:

UPDATE(
  SELECT Ord.Completed
  FROM Product P
  INNER JOIN Order1 Ord
  ON Ord.OrderID = P.OrderID
  WHERE EXISTS(
          SELECT *
          FROM Delivery D
          WHERE Delivery.Delivered = 0 AND P.ProductID = Delivery.DeliveryID
        )
)
SET Completed= 'NO';

If I run the SELECT part only, without UPDATE it returns the right results. When I try to execute the UPDATE query I get

"ORA-00933: SQL command not properly ended
00933. 00000 -  "SQL command not properly ended"
*Cause:    
*Action:
Error at Line: 2 Column: 250"

Any ideas?