iPhone - Replacing rootview in navigation controller

I have a project with a NavigationController, that contains into IB the first ViewController to show. That's just the default pattern when creating the project.

In that first viewController, I receive some event that I send to the appDelegate, and I want it to replace that rootview with another one. Not going to a next one.

So I do :

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{   
    // Override point for customization after application launch.
    // Add the navigation controller's view to the window and display.
    self.window.rootViewController = self.navigationController;
    [self.window makeKeyAndVisible];
    return YES;
}

- (void) goNext {

    [self.navigationController popViewControllerAnimated:NO];

    NextViewController* nextWindow = [[[NextViewController alloc] initWithNibName:@"NextView" bundle:nil] autorelease];
    [self.navigationController pushViewController:nextWindow animated:NO];
}

But that doesn't work, the first viewcontroller is not poped. And the second one is logically displayed with a back button.

I just want to replace that first view with the other one as the start of the navigation process.