How the Model changes could be notified to ViewModel in MVVM?

Thanks Shmuel Zang for your reply.

I have implemented the INotifyPropertyChanged in the model and subscribed the PropertyChanged event of the model in my ViewModel. It works.

As we know that by applying [CallerMemberName] attribute (used in OnPropertyChanged()), we avoid the "Rename Refactoring doesn't change the String values" problem. I would like to know that is there any mechanism like [CallerMemberName] attribute to avoid the same problem ("Rename Refactoring doesn't change the String values") which may happen in the myModel_PropertyChanged() event handler in my ViewModel?
(exaclty here in the code: if (e.PropertyName == "MyFirstName"))

Here is my code:

internal class Model:INotifyPropertyChanged
    {
        public Model()
        {
        }

        string _FirstName = "Shahir";
        public string FirstName
        {
            get { return _FirstName; }
            set
            {
                _FirstName = value;
                OnPropertyChanged();
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;

        private void OnPropertyChanged([CallerMemberName] string propertyName = "")
        {
            if(PropertyChanged!=null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }
    }

internal class MyViewModel:INotifyPropertyChanged
    {
        private Model myModel;

        public MyViewModel(Model model)
        {
            this.myModel = model;
            myModel.PropertyChanged += myModel_PropertyChanged;
        }


        public event PropertyChangedEventHandler PropertyChanged;

        private void OnPropertyChanged([CallerMemberName] string propertyName = "")
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }


        string _FirstName;
        public string MyFirstName
        {
            get { return myModel.FirstName; }
            set
            {
                _FirstName = value;
                OnPropertyChanged();
            }
        }

        private void myModel_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
        {
            if (e.PropertyName == "FirstName")
            {
                MyFirstName = myModel.FirstName;
            }
        }
    }