Swift 3更新位置注释

例如，这个红色指针的坐标现在是：51.507222，-0.1275。我想换一下这张照片的底片。我该怎么做

class Capital: NSObject, MKAnnotation {
    var title: String?
    var coordinate: CLLocationCoordinate2D
    var info: String

    init(title: String, coordinate: CLLocationCoordinate2D, info: String) {
        self.title = title
        self.coordinate = coordinate
        self.info = info
    }
}

let london = Capital(title: "London", coordinate: CLLocationCoordinate2D(latitude: 51.507222, longitude: -0.1275), info: "Home to the 2012 Summer Olympics.")

@IBOutlet weak var mapView: MKMapView!


override func viewDidLoad() {
    super.viewDidLoad()

    mapView.addAnnotations([london])
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

}

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能否添加所需内容的更多详细信息。如果要更改坐标

london.coordinate=newLocation