Allow players to save the new AllowedWords back into aqawords.txt

The first thing you should do is find the method which loads the AllowedWords:

        private static void LoadAllowedWords(ref List<string> AllowedWords)
        {
            try
            {
                StreamReader FileReader = new StreamReader("aqawords.txt");
                while (!FileReader.EndOfStream)
                {
                    AllowedWords.Add(FileReader.ReadLine().Trim().ToUpper());
                }
                FileReader.Close();
            }
            catch (Exception)
            {
                AllowedWords.Clear();
            }
        }

We are going to follow this structure but change everything to write instead of reading the files. Firstly create a new method:

        private static void SaveAllowedWords(ref List<string> AllowedWords)
        {

        }

Now to setup the file writer:

        private static void SaveAllowedWords(ref List<string> AllowedWords)
        {
                StreamWriter FileWriter = new StreamWriter("aqawords.txt");


                FileReader.Close();
        }

Now we need a loop to cycle through each allowed word, and write it to the file:

        private static void SaveAllowedWords(ref List<string> AllowedWords)
        {
            StreamWriter FileWriter = new StreamWriter("aqawords.txt");

            foreach (string word in AllowedWords)
            {
                FileWriter.WriteLine(word);
            }
            FileWriter.Close();
        }

To keep the file in order we could also sort the list of allowed words before we write it:

        private static void SaveAllowedWords(ref List<string> AllowedWords)
        {
            StreamWriter FileWriter = new StreamWriter("aqawords.txt");
            AllowedWords.Sort();

            foreach (string word in AllowedWords)
            {
                FileWriter.WriteLine(word);
            }
            FileWriter.Close();
        }

You might want to specify a file name, so you could use readline to get the file name:

         private static void SaveAllowedWords(ref List<string> AllowedWords)
        {
            string filename = "";
            do
            {
                Console.WriteLine("Please enter a filename: ");
                filename = Console.ReadLine();
            }
            while (filename == "");

            StreamWriter FileWriter = new StreamWriter(filename);
            AllowedWords.Sort();

            foreach (string word in AllowedWords)
            {
                FileWriter.WriteLine(word);
            }

            FileWriter.Close();
        }