How to display next letter using button in c#

Question

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace WindowsFormsApplication31
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void A(object sender, EventArgs e)
{
// display G
int row, column;
for (row = 0; row <= 6; row++)
{
for (column = 0; column <= 6; column++)
{
if ((column == 1 && row != 0 && row != 6) || ((row == 0 || row == 6) && column > 1 && column < 5) || (row == 3 && column > 2 && column < 6) || (column == 5 && row != 0 && row != 2 && row != 6))
textBox1.AppendText("*");
else
textBox1.AppendText(" ");
}
textBox1.AppendText(Environment.NewLine);
}
textBox1.AppendText(Environment.NewLine);
//Here i want a code so that when i click on my button it will display next letter
//DISPLAY Z
for (row = 0; row <= 6; row++)
{
for (column = 0; column <= 6; column++)
{
if (((row == 0 || row == 6) && column >= 0 && column <= 6) || row + column == 6)
textBox1.AppendText("*");
else
textBox1.AppendText(" ");
}
textBox1.AppendText(Environment.NewLine);
}
textBox1.AppendText(Environment.NewLine);
}
}
}

Here is my code and i want display letter by clicking button .when i click on button for first time it should display G and when i click for second time it should display Z.