If you are adding constraint programatically like this:

var constraintButton =NSLayoutConstraint(item: buttonPlay, 
                                           attribute:NSLayoutAttribute.Bottom, 
                                           relatedBy:NSLayoutRelation.Equal, 
                                           toItem
 
:self.view, 
                                           attribute:NSLayoutAttribute.Bottom, 
                                           multiplier:1,
                                           constant:0)// Add the constraint to the viewself.view.addConstraint(constraintButton)

Then you can update it this way:

self.constraintButton.constant =50self.view.layoutIfNeeded()

And if you want that with animation you can do it this way:

self.view.layoutIfNeeded()UIView.animateWithDuration(1, animations:{self.constraintButton.constant =50self.view.layoutIfNeeded()})