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 = 50    self.view.layoutIfNeeded()})

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 = 50    self.view.layoutIfNeeded()})