After upload the image without reducing the size in asp.net...?

protected void Button1_Click(object sender, EventArgs e)
   {
       FileName = Guid.NewGuid().ToString();
       FilePath = @"C:\Users\bravemountravi\Desktop\Image\Attachments\" + FileName + "." + "jpg";

       System.Drawing.Image Mainimg = System.Drawing.Image.FromFile(@"C:\Users\travi\Desktop\Image\Attachments\funny-dog-wallpaper-and-picture-p0d-funny-dog-photo-hd-ahhw.jpg");

           System.Drawing.Image img2 = System.Drawing.Image.FromFile(@"C:\Users\travi\Desktop\Image\Images\watermark3.png");

           Graphics g = Graphics.FromImage(Mainimg);



           double _scalefactor = (Mainimg.Width / 4800.0);

           if (_scalefactor <= 0.1)
           {
               _scalefactor = 0.1;
           }
           else    if (_scalefactor <= 0.2)
           {
              _scalefactor = 0.2;
           }

           else if (_scalefactor >= 1)
           {
               _scalefactor = 1.0;
           }


           double _newwidth = (_scalefactor * img2.Width);
           //double _newHeight = ((_newwidth / img2.Width) * (img2.Height));

           double _newHeight = (_scalefactor * img2.Height);


           Bitmap bitimg = WaterMarkScaleImage(img2, Convert.ToInt32(Math.Round(_newwidth, 0)), Convert.ToInt32(Math.Round(_newHeight, 0)));
           System.Drawing.Image scaleimg = (System.Drawing.Image)bitimg;


           int left = Mainimg.Width - scaleimg.Width;
           int top = Mainimg.Height - scaleimg.Height;

         g.DrawImage(scaleimg, left, top, scaleimg.Width, scaleimg.Height);

           g.Dispose();
          Mainimg.Save(FilePath);

   }
   public Bitmap WaterMarkScaleImage(System.Drawing.Image image, int maxWidth, int maxHeight)
   {
       var newImage = new Bitmap(maxWidth, maxHeight);
       Graphics.FromImage(newImage).DrawImage(image, 0, 0, maxWidth, maxHeight);
       Bitmap bmp = new Bitmap(image);
       return bmp;
   }