how to reduce the image file size

hi if (FileUpload1.HasFile)
            {
                string savePath = Server.MapPath("~/memberspic/");
                string fileName = FileUpload1.FileName;
                string pathToCheck = savePath + fileName;
                Random rm = new Random();
                TextBox txtpass = new TextBox();
                txtpass.Text = rm.Next(257871, 498371).ToString();
                string extension = Path.GetExtension(FileUpload1.PostedFile.FileName);
                //FileUpload1.SaveAs(savePath + "img_pk" + txtpass.Text.ToString() + extension);
                FileUpload1.SaveAs(Server.MapPath("~/memberspic/") + "img_pk" + txtpass.Text.ToString() + extension);
                string te;
                te = "~/memberspic/" + "img_pk" + txtpass.Text.ToString() + extension;
               
                // }
by using above code we can upload the images in to folder.
but i want to reduce the file size before when i save the file into folder please help me