gistfile1.txt

var childVC: UIViewController?
@IBOutlet weak var containerView: UIView!

func ChangeViewController() { 
    childVC?.willMoveToParentViewController(nil)
    childVC?.view.removeFromSuperview()
    childVC?.removeFromParentViewController()
    childVC = storyboard?.instantiateViewControllerWithIdentifier("identifier") as? UIViewController
    if let childVC = childVC {
        addChildViewController(childVC)
        childVC.view.frame = containerView.bounds 
        containerView.addSubview(childVC.view)
        childVC.didMoveToParentViewController(self)
    }
}