How do I store data in a buffer?

using System;
using System.Net;
using System.IO;
using System.Text;
using System.Net.Sockets;
using System.Diagnostics;
using System.Runtime.Remoting;
using System.Runtime.Remoting.Messaging;


namespace ProjectEnvironmentVariableUpd
{
    class Program
    {
        static void Main(string[] args)
        {



            BasicFTPClient MyClient = new BasicFTPClient();

            MyClient.Host = "[removed to protect user]";
            MyClient.Username = "[removed to protect user]";
            MyClient.Password = "[removed to protect user]";

            try
            {
                MyClient.DownloadFile("test.txt"); // c:\temp\mydownload.txt for Windows
            }
            catch (WebException e)
            {
                Console.WriteLine(e.ToString());
            }
        }

    }

    class BasicFTPClient
    {
        public string Username;
        public string Password;
        public string Host;
        public int Port;

        public BasicFTPClient()
        {
            Username = "[removed to protect user]";
            Password = "[removed to protect user]";
            Port = 21;
            Host = "[removed to protect user]";
        }

        public BasicFTPClient(string theUser, string thePassword, string theHost)
        {
            Username = theUser;
            Password = thePassword;
            Host = theHost;
            Port = 21;
        }

        private Uri BuildServerUri(string Path)
        {
            return new Uri(String.Format("ftp://{0}:{1}/{2}", Host, Port, Path));
        }


        /// <summary>
        /// This method downloads the given file name from the FTP server
        /// and returns a byte array containing its contents.
        /// Throws a WebException on encountering a network error.
        /// </summary>

        public string DownloadData(string path)
        {
            // Get the object used to communicate with the server.
            WebClient request = new WebClient();

            // Logon to the server using username + password
            request.Credentials = new NetworkCredential(Username, Password);
            
            // return a string

            byte[] data = request.DownloadData(BuildServerUri(path));
            
            string data2 ="";

            // see a other solution to convert byte into string

            for (int i=0;i <data.Length;i++)
            {
             data2 += (char)data[i]; 
            }
            return data2;
        }


        /// <summary>
        /// This method downloads the FTP file specified by "ftppath" and saves
        /// it to "destfile".
        /// Throws a WebException on encountering a network error.
        /// </summary>
        public void DownloadFile(string ftppath)
        {
            // Download the data
            string Data = DownloadData(ftppath);


            // convert data in string




            // Save the data to RAM in buffer
            //buffer size was automatically set to the default size of the defined data buffer, 1024 byte
            string[] Data = new byte[1024];
           


            // download data file test.txt in ram buffer and add or del enviroment variable



            // be carreful don't erase other values in environement variable

           
            
            Console.WriteLine(Data);
        }

            
        // get enviroment variables in Data and their value and action





        static void ShowEnvironmentVariables()
        {
            // Get and display the value of PATH
            string sPathValue = Environment.GetEnvironmentVariable("path");
            Console.WriteLine("PATH = {0}", sPathValue);

            // Show all environment variables
            Console.WriteLine("Machine environment variables:");
            IDictionary env = Environment.GetEnvironmentVariables(EnvironmentVariableTarget.Machine);
            foreach (DictionaryEntry var in env)
            {
                Console.WriteLine("\t{0} = {1}", var.Key, var.Value);
            }
        }
   
        
        // update / dell / add enviroment variables in Data and their value include action



            //Console.ReadKey(true);