I usually use a class Singleton to work the Stage. So to switch between screens in the controllers call the method loadNewStage of my class responsible for working the Stage. 
Havestage class
public class HaveStage {
    private static HaveStage haveStage = null;
    private Stage stage;
    private HaveStage(Stage stage) {
        this.stage = stage;
    }
    public static HaveStage instance(Stage stage) {
        if (haveStage == null) {
            haveStage = new HaveStage(stage);
        }
        return haveStage;
    }
    public Stage getStage() {
        return this.stage;
    }
    public void loadNewStage(Parent fxmlLoad) {
        if (stage != null) {
            Parent root = fxmlLoad;
            Scene scene = new Scene(root);
            stage.setScene(scene);
            //stage.show();
        }
    }
}
Application class
public class MinhaClasse extends Application {
    private HaveStage haveStage;
    @Override
    public void start(Stage stage) {
        this.haveStage = HaveStage.instance(stage);
        Parent root = null;
        Scene scene;
        try {
            root = FXMLLoader.load(getClass().getResource("/br/com/projeto/primeiraTela.fxml"));
        } catch (IOException ex) {
            Logger.getLogger(MinhaClasse.class.getName()).log(Level.SEVERE, null, ex);
        }
        scene = new Scene(root);
        haveStage.getStage().setScene(scene);
        haveStage.getStage().show();
    }
}
Whenever you want to switch the screen call the method loadNewStage in the controllers.
Controller Example
public class LoginScreenController {
    @FXML
    void login(InputEvent event) {
        try {
            Parent temp = FXMLLoader.load(getClass().getResource("/br/com/projeto/segundaTela.fxml"));
            changeScreen(temp);
        } catch (IOException ex) {
            ex.getCause().printStackTrace();
            new Notifications().errorNotification("Erro ao carregar nova tela!");
        }
    }
    private void changeScreen(Parent fxmlLoad) {
        HaveStage.instance(null).loadNewStage(fxmlLoad);
    }
}
							
							
						 
Hi @Ronaldo Alves. It is beneficial for the community to give a feedback if the problem has been solved or if it still remains. I left an answer but you did not give a return.
– Paulo Weverton