Sql update query question

I have a query that does some calculations from two tables and I want to up date one of the tables valus from the result of that query.  now how do i update the stock table field [quanity in stock] and altinstkqty from this query where [stock id] = [stock id]
SELECT
Stock.[Stock ID],
Case when tbl_RESPAR_REPLACE.RESPAR_QTY_MFG > 0 then
Stock.[Quanity in Stock] - tbl_RESPAR_REPLACE.RESPAR_QTY_MFG
else 0
end as newMfgQTy,
Case when tbl_RESPAR_REPLACE.RESPAR_QTY_ALT > 0 then
Stock.AltInStkQty - tbl_RESPAR_REPLACE.RESPAR_QTY_ALT
else 0
end as newAltQty
FROM tbl_RESPAR_REPLACE INNER JOIN
 Stock ON tbl_RESPAR_REPLACE.RESPAR_STOCKID = Stock.[Stock ID]
WHERE     (tbl_RESPAR_REPLACE.RESPAR_RESREQID = 1)
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