If i wanted to turn my application into OOP design hows the best way to do it

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using Microsoft.Win32;
 
namespace PC_Audit {
	public partial class Form1 : Form {
		public Form1() {
			InitializeComponent();
		}
 
		private void Form1_Load(object sender, EventArgs e) {
 
		}
 
		private void btnClose_Click(object sender, EventArgs e) {
			this.Close();
		}
 
		private void btnLoad_Click(object sender, EventArgs e) {
			GetInstalledApps();
		}
 
		public void GetInstalledApps() {
			treeView1.Nodes.Clear();
 
			string uninstallKey = (@"SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall");
 
			RegistryKey rk = Registry.LocalMachine.OpenSubKey(uninstallKey);
 
			string[] skNames = rk.GetSubKeyNames();
 
			// for each installed program
			foreach (string skName in rk.GetSubKeyNames()) {
 
				RegistryKey sk = rk.OpenSubKey(skName);
 
				object displayName = sk.GetValue("DisplayName");
				object value;
 
				value = sk.GetValue("ParentKeyName");
 
				if ((displayName != null) && (value == null)) {
 
					TreeNode nd1 = treeView1.Nodes.Add(displayName.ToString()); //Root
 
					// add extra info to node
					value = sk.GetValue("DisplayVersion");
					if (value != null) nd1.Nodes.Add(value.ToString());
				}
			}
			treeView1.Sort();
		}
 
		private System.IO.StreamWriter sw;
 
		private void saveToolStripMenuItem_Click(object sender, EventArgs e) {
			saveFileDialog1.Title = "Specify Destination File Name";
			saveFileDialog1.Filter = "Text Files (*txt)|*.txt";
			saveFileDialog1.FilterIndex = 1;
			saveFileDialog1.OverwritePrompt = true;
			saveFileDialog1.FileName = "InstalledApps_" + SystemInformation.ComputerName + "_" + DateTime.Now.ToString("yyyymmdd") ;
			saveFileDialog1.InitialDirectory = Application.StartupPath;
 
			if ((saveFileDialog1.ShowDialog() != DialogResult.Cancel)) {
				txtDestination.Text = saveFileDialog1.FileName;
				System.IO.FileStream fs = new System.IO.FileStream(saveFileDialog1.FileName, System.IO.FileMode.OpenOrCreate, System.IO.FileAccess.Write, System.IO.FileShare.ReadWrite);
				sw = new System.IO.StreamWriter(fs, System.Text.Encoding.ASCII);
				foreach (TreeNode nd in treeView1.Nodes) {
					sw.WriteLine(GetNodeTexts(nd));
				}
 
 
				sw.Close();
			}
		}
 
		// get textual representation of node
		private string GetNodeTexts(TreeNode node) {
			return node.Text;
		}
	}
}