You can do this:
public void ResizeImage(string fileName, int width, int height)
{
using (Image image = Image.FromFile(fileName))
{
new Bitmap(image, width, height).Save(fileName);
}
}
If its a new file just replace with this or with a custom path of your choosing:
new Bitmap(image, width, height).Save(fileName.Insert(fileName.LastIndexOf('.'),"A"));