Calling Function from another class swift

Im having trouble calling a function in my GameViewController.swift from another class, Menu.swift. I call the function like this:

class Menu: SKnode {

    func scoreAction(sender:UIButton!) { 
        self.buttonPlay.removeFromSuperview()
        self.buttonScore.removeFromSuperview()
         // CALLING FUNCTION
        GameViewController.showLeaderboard()    
     }
}

And here is the function I'm trying to call:

class GameViewController: UIViewController,
 UITextFieldDelegate, GKGameCenterControllerDelegate  {

   func showLeaderboard()
    {
      var gcViewController: GKGameCenterViewController = GKGameCenterViewController()
      gcViewController.gameCenterDelegate = self

      gcViewController.viewState = GKGameCenterViewControllerState.Leaderboards
      gcViewController.leaderboardIdentifier = "yourleaderboardid"

      self.presentViewController(gcViewController, animated: true, completion: nil)
    }

}

I have a Compiler Error inside my Menu class in the line GameViewController.showLeaderboard() "Missing argument for parameter #1 in call" But I don't understand what type of argument the compiler is expecting because I declared the function without any needing any parameters.

Thank you

In GameViewController you have defined scoreAction as instance method not the class function.You should call scoreAction by making instance of GameViewController

class Menu: SKnode {

    func scoreAction(sender:UIButton!) { 
        self.buttonPlay.removeFromSuperview()
        self.buttonScore.removeFromSuperview()
         // CALLING FUNCTION 
         //see () on GameViewController
        GameViewController().showLeaderboard()    
     }
}

I think you should load GameViewController from storyBoard if you have GameViewController in storyBoard