try this one :
declare @colA varchar(50),@colB varchar(50),@colC varchar(50)
select @colA=colA,@colB=colB,@colC=colC from tblX
where id = '1' -- this is the one that you want to get the data from
update tblX
set colA=@colA,colB=@colB,colC=@colC
where id <> '1'