Update Query with Join

select * from S_products where Serial in 
(
select Max(serial)as Serial
FROM S_products A where StoreCode='DEIRA' and ItemCode in (select ItemCode from PUBS..DEIRAVARIANCE16122013) group by ItemCode
)

the above Query result I am getting results

Serial,ItemCode,qty,abgprice 

Now I want to update qty= qty+varientqty

Another Table : StoreExcel, It has ItemCode,varientqty

So I want to Join the abov atable with abov query and update the qty corresponding to itemcode

Please format tht query

AK