Editing image field in gridview by fileUpload

Hi

 I have two columns in gridview which I want to use template for editing them( web column and image column)

for web column editing I used two textBox as template.one for name of web and another for address.

the code is here:

  string siteNm = ((TextBox)GridView1.Rows[e.RowIndex].Cells[16].Controls[1]).Text;
string siteAddr = ((TextBox)GridView1.Rows[e.RowIndex].Cells[16].Controls[3]).Text;

and for updating information 

  SqlConnection con = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings[2].ToString());
SqlCommand cmd = new SqlCommand("update students set stu_img=@7, stu_web_name=@8 , stu_web_addr=@9", con);
cmd.Parameters.AddWithValue("@8", siteNm);
cmd.Parameters.AddWithValue("@9", siteAddr);

con.Open();
cmd.ExecuteNonQuery();
con.Close();
GridView1.EditIndex = -1;
sel();

Now I want to edit image column by fileUpload...I don't know how to write code of this?