In case of simple hyperlink to download the File(where you put it on server) Just put the link to that file i.e. Download. it will be down loaded automatically in virtual server.
ex:- Same as
DigitalMan suggested you
in case of you are not using hyperlink i.e. using Button or ImageButton then code will be on
Downloading.aspx.vc
and it should be look like
Response.Redirect("URLofFile")
fore more details take a look
there[
^]