How can I update the MKMapView?

Question

I can use this method to show my location at first.

-(void)displayRegion:(double)latitudeDouble: (double)longitudeDouble{
    CLLocationCoordinate2D coord = {latitude: latitudeDouble, longitude: longitudeDouble};

    MKCoordinateSpan span = {latitudeDelta: .005, longitudeDelta: .005};
    MKCoordinateRegion region = {coord, span};
    [myMKMapView setRegion:region animated:TRUE];   
    [myMKMapView regionThatFits:region];
}

But after I loaded it, it can't update my map again. I want to update myMKMapView again. plz help. thx a lot.