ChangeFileName

        public static string ChangeFileName(string path, string name)
        {
            string directoryName = Path.GetDirectoryName(path);
            string fileNameWithoutExtension = Path.GetFileNameWithoutExtension(path);
            string extension = Path.GetExtension(path);

            string nameWExtension = string.Format("{0}.{1}", name, extension.Trim('.'));

            string fullPath = Path.Combine(directoryName, nameWExtension);
            return fullPath;
        }