def METHOD_NAME(self, lens_model_class):
    """Update LensModel() and LensEquationSolver() instance.
    :param lens_model_class: LensModel() class instance
    :return: internal lensModel class updated
    """
    self._lens_model = lens_model_class
    if lens_model_class is None:
        self._solver = None
    else:
        self._solver = LensEquationSolver(lens_model_class)