Select distinct rows based on latest date

SELECT * from (SELECT c.client_no,
       c.forename,
       c.surname,
       c.tel_no1,
       c.tel_no2,
       c.tel_no3,
       o.ordernumber,
       o.propertyidentifier,
       o.contractorlongname,
       o.OrderStatus,
       o.CancelReasonDesc,
       o.OriginationDate,
       o.Completed,
       Datediff(d, o.OriginationDate, Getdate()) AS Total

           ,Row_number() Over(Partition by c.client_no Order by  o.Completed  DESC ) rn

FROM   hgmclent AS c
       LEFT OUTER JOIN QLHPM_Order_Summary AS o
                    ON c.client_no = o.ClientNumber
WHERE  o.Ordernumber IS NOT NULL
 ) t
 WHERE rn=1