A standalone plugin(snippet) that checks version information and extracts a ZIP download

Act_Plugin_Update2.cs

public void InitPlugin(TabPage pluginScreenSpace, Label pluginStatusText)
{
	ActGlobals.oFormActMain.UpdateCheckClicked += oFormActMain_UpdateCheckClicked;
	if (ActGlobals.oFormActMain.GetAutomaticUpdatesAllowed())   // If ACT is set to automatically check for updates, check for updates to the plugin
		new Thread(new ThreadStart(oFormActMain_UpdateCheckClicked)) { IsBackground = true }.Start();   // If we don't put this on a separate thread, web latency will delay the plugin init phase
}
public void DeInitPlugin()
{
	ActGlobals.oFormActMain.UpdateCheckClicked -= oFormActMain_UpdateCheckClicked;
}
void oFormActMain_UpdateCheckClicked()
{
	int pluginId = 999;    // This ID must be the same ID used on ACT's website.  
	try
	{
		Version localVersion = this.GetType().Assembly.GetName().Version;
		Version remoteVersion = new Version(ActGlobals.oFormActMain.PluginGetRemoteVersion(pluginId).TrimStart(new char[] { 'v' }));    // Strip any leading 'v' from the string before passing to the Version constructor
		if (remoteVersion > localVersion)
		{
			Action updateAction = new Action(() =>       // Action we perform when told to update
			{
				// You could use a MessageBox for this as well
				TraySlider slider = new TraySlider();
				slider.ShowDurationMs = 60000;
				slider.ButtonLayout = TraySlider.ButtonLayoutEnum.TwoButton;
				slider.ButtonSE.Text = "Ignore";
				slider.ButtonSW.Text = "Update";
				slider.ButtonSW.Click += (s, e) =>
				{
					FileInfo updatedFile = ActGlobals.oFormActMain.PluginDownload(pluginId);
					ActPluginData pluginData = ActGlobals.oFormActMain.PluginGetSelfData(this);
					pluginData.pluginFile.Delete();

					ActGlobals.oFormActMain.UnZip(updatedFile.FullName, pluginData.pluginFile.DirectoryName);

					// You can choose to simply restart the plugin, if the plugin can properly clean-up in DeInit and has no external assemblies that update
					ThreadInvokes.CheckboxSetChecked(ActGlobals.oFormActMain, pluginData.cbEnabled, false); // Deinit the old plugin
					Application.DoEvents();
					ThreadInvokes.CheckboxSetChecked(ActGlobals.oFormActMain, pluginData.cbEnabled, true);  // Init the new version

					// OR, you can request that ACT be restarted when the user accepts
					ActGlobals.oFormActMain.RestartACT(true, "The PLUGINNAME plugin requires ACT to be restarted to work properly.");
				};
				slider.ShowTraySlider("There is an updated version of the PLUGINNAME Plugin.  Update it now?\n\n(If there is an update to ACT, you should click No and update ACT first.)", "New Version");
			});

			if (ActGlobals.oFormActMain.InvokeRequired)	// TraySliders must be created on the UI thread
				ActGlobals.oFormActMain.Invoke(updateAction);
			else
				updateAction.Invoke();
		}
	}
	catch (Exception ex)
	{
		ActGlobals.oFormActMain.WriteExceptionLog(ex, "Plugin Update Check");
	}
}