Файл StreamReader, как обновлять ТОЛЬКО при достижении высокого балла в списке?

Как мне написать файл StreamReader, в котором он будет переопределять рекорд игры, ТОЛЬКО если он выше текущего рекорда? В настоящее время все оценки обновляются в списке, а не только те оценки, которые превышают текущий файл score/txt.

Заранее спасибо

public partial class Form1 : Form
{
    int Dice;
    int RunningTotal;
    int MaxRolls;
    int RollCount;
    Random rand = new Random();

    public Form1()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        RollDiebutton.Enabled = true;
        StartOverbutton.Enabled = true;
        ClickBeginGametoStartlabel.Visible = false;
        int beginTotal = 0;
        TotalMoneyEarnedlabel.Text = beginTotal.ToString("c");

        MaxRolls = rand.Next(3) + 2;
    }

    private void button4_Click(object sender, EventArgs e)         
    {
        try
        {
            string highScore;
            StreamReader inputFile; 

            inputFile = File.OpenText("Highscore.txt"); 
            HighscoreBox.Items.Clear();

            while (!inputFile.EndOfStream)
            {
                highScore = inputFile.ReadLine();   
                HighscoreBox.Items.Add(highScore);
            }

            inputFile.Close();
        }

        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }

        RollDiebutton.Enabled = false;
        BeginGamebutton.Enabled = true;
        StartOverbutton.Enabled = false;
        TotalMoneyEarnedlabel.Text = "";

        BeginpictureBox.Image = P2Kbembow.Properties.Resources.Begin;
        Pressyourluckandrollagainlabel.Visible = false;
        ClickBeginGametoStartlabel.Visible = true;
    }

    private void button2_Click(object sender, EventArgs e)
    {
        //Close Form
        this.Close();
    }

    private void RollDiebutton_Click(object sender, EventArgs e)
    {
        Random rand = new Random();
        Dice = rand.Next(6) + 1;

        RunningTotal += 0;
        int DollarAmount = 100;
        int Sum = (Dice * DollarAmount);

        BeginGamebutton.Enabled = false;
        Pressyourluckandrollagainlabel.Visible = true;

        RunningTotal += Sum;
        TotalMoneyEarnedlabel.Text = RunningTotal.ToString("c");
        RollCount += 1;

        if (MaxRolls == 0)
        {
            Random getMax = new Random();
            TotalMoneyEarnedlabel.Text = ""; 
        }
        else
            if (RollCount >= MaxRolls)
            {
                MaxRolls = 6;
                RollCount = 0;
                RunningTotal = 0;

                TotalMoneyEarnedlabel.Text = "$0.0";
                Show(); MessageBox.Show("Sorry! You lose!");

                RollDiebutton.Enabled = false;
                BeginGamebutton.Enabled = true;

                TotalMoneyEarnedlabel.Text = "";

                BeginpictureBox.Image = P2Kbembow.Properties.Resources.Begin;
                Pressyourluckandrollagainlabel.Visible = false;
                ClickBeginGametoStartlabel.Visible = true;
                StartOverbutton.Enabled = false;

                return;
            }

        StreamWriter outputFile;
        outputFile = File.CreateText("HighScore.txt");

        outputFile.WriteLine(TotalMoneyEarnedlabel.Text);
        outputFile.Close();

        if (Dice == 1)
        {
            //shows Image of dice 1
            BeginpictureBox.Image = P2Kbembow.Properties.Resources._1Die;
        }

        if (Dice == 2)
        {
            //shows Image of dice 2
            BeginpictureBox.Image = P2Kbembow.Properties.Resources._2Die;
        }

        if (Dice == 3)
        {
            //shows Image of dice 3
            BeginpictureBox.Image = P2Kbembow.Properties.Resources._3Die;
        }
        if (Dice == 4)
        {
            //shows Image of dice 4
            BeginpictureBox.Image = P2Kbembow.Properties.Resources._4Die;
        }

        if (Dice == 5)
        {
            //shows Image of dice 5
            BeginpictureBox.Image = P2Kbembow.Properties.Resources._5Die;
        }

        if (Dice == 6)
        {
            //shows Image of dice 6
            BeginpictureBox.Image = P2Kbembow.Properties.Resources._6Die;
        }

        //Display Message Box of dice rolled 
        Show(); MessageBox.Show(" You rolled a  " + Dice + "!");
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        try
        {
            string highScore;
            StreamReader inputFile;

            inputFile = File.OpenText("Highscore.txt");
            HighscoreBox.Items.Clear();

            while (!inputFile.EndOfStream)
            {
                highScore = inputFile.ReadLine();
                HighscoreBox.Items.Add(highScore);

            }

            inputFile.Close();
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }    
    }
}