c# Socket class server and client both to send and receive

I'm creating a project in which I have to use Socket class to send asynchronous messages in c#.

I've created the project with a client connecting to a server and the client sending messages to server, but now i want the server to respond another byte[] to client with the same socket, but I don't find how to do it, and I performed some tests but it is not working.

As example, now I hace something like that (I reduced it to the base just for you to understand where I am):

Client:

namespace Client
{
    public partial class Client : Form
    {
        private Socket _clientSocket;
        private byte[] _buffer;

        public Client()
        {

            InitializeComponent();
        }

        public void btnConnect_Click(object sender, EventArgs e)
        {
            _clientSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            _clientSocket.BeginConnect(new IPEndPoint(IPAddress.Loopback, 3333), new AsyncCallback(ConnectCallback), null);
        }
        private void ConnectCallback(IAsyncResult AR)
        {

            _clientSocket.EndConnect(AR);

        }
        private void btnSend_Click(object sender, EventArgs e)
        {
            string xmlstring = "test";
            byte[] xmlbuffer = Encoding.ASCII.GetBytes(xmlstring);
            _clientSocket.BeginSend(xmlbuffer, 0, xmlbuffer.Length, SocketFlags.None, new AsyncCallback(SendCallback), null);
        }
        private void SendCallback(IAsyncResult AR)
        {
            _clientSocket.EndSend(AR);
            _buffer = new byte[_clientSocket.ReceiveBufferSize];
        }
    }
}

Server:

namespace Server
{
    public partial class Server : Form
    {
        private Socket _serversocket, _clientSocket;
        private byte[] _buffer;

        public Server()
        {
            InitializeComponent();
            StartServer();

        }

        private void StartServer()
        {
            _serversocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            _serversocket.Bind(new IPEndPoint(IPAddress.Any, 3333));
            _serversocket.Listen(0);
            _serversocket.BeginAccept(new AsyncCallback(AcceptCallback), null);
        }

        private void AcceptCallback(IAsyncResult AR)
        {
            _clientSocket = _serversocket.EndAccept(AR);
            _buffer = new byte[_clientSocket.ReceiveBufferSize];
            _clientSocket.BeginReceive(_buffer, 0, _buffer.Length, SocketFlags.None, new AsyncCallback(ReceiveCallback), null);
            _serversocket.BeginAccept(new AsyncCallback(AcceptCallback), null);
        }

        private void ReceiveCallback(IAsyncResult AR)
        {
            int received = _clientSocket.EndReceive(AR);
            Array.Resize(ref _buffer, received);
            string text = Encoding.ASCII.GetString(_buffer);
            Array.Resize(ref _buffer, _clientSocket.ReceiveBufferSize);
        }
    }
}

I tried to send an answer the other way arround but it did not work, so I would like to ask you how to do it.

Thanks, and sorry if the post is not right, as it is my first one.