Openfiledialog lock my file :/

Hello,

i'm new in the programming world and i try to create a small program who can modify a simple ini file with different ligne i need to change with textbox.

The problem is i use an openfiledialog. I can open and use the file but after i need to modify that file but it's seems that the openfiledialog lock the file and i can't modify anything in that file !

 public partial class Form1 : Form
    {
        List<string> site = new List<string>();
        List<string> Read_fileTAB = new List<string>();
        string section = "";
        string Garg1 = "";
        string Garg2 = "";
        string Garg3 = "";
        string Garg4 = "";
        string link_Read1 = "";
        string chemin_fichier1 = "";
        string nom_fichier1 = "";
        int arg1_pos = 0;
        int arg2_pos = 0;
        int arg3_pos = 0;
        int arg4_pos = 0;

        public Form1()
        {
            InitializeComponent();
            
        }


        private void ouvrirToolStripMenuItem_Click(object sender, EventArgs e)
        {

            OpenFileDialog openFileDialog1 = new OpenFileDialog();
            openFileDialog1.InitialDirectory = "c:\\";
            openFileDialog1.Filter = "Fichier de configuration FTP INI (*.ini)|*.ini|All files (*.*)|*.*";
            openFileDialog1.RestoreDirectory = false;
            openFileDialog1.ShowHelp = true;
            openFileDialog1.ShowReadOnly = true;

            if (openFileDialog1.ShowDialog() == DialogResult.OK)
            {
                try
                {
                    if (openFileDialog1.OpenFile() != null)
                    {
                        //MessageBox.Show("Fichier ouvert correctement");

                        chemin_fichier1 = openFileDialog1.FileName;
                        //new FileStream(chemin_fichier1, FileMode.Open, FileAccess.ReadWrite);
                        Read_file(chemin_fichier1,"[FTP-SETTINGS]", "Site", "port", "login", "password");
                        openFileDialog1.Dispose();
                    }
                }
                catch (Exception ex)
                {
                    MessageBox.Show("Error: Could not read file from disk. Original error: " + ex.Message);
                }
            }

        }

Thank you for your reply