Supposing I have an OWL class class_1 with subclasses: sub_1, sub_2, sub_3, how do I turn sub_1, sub_2, sub_3 into subclasses of a new class named new_class, and make new_class to be subclass of class_1 ? I am googling it, without any success...
You can add new_class as a subclass of class_1 by selecting class_1 and clicking on the add class button. You can then select the other classes you wish to modify and add new_class as a superclass (the options are available in the detail pane). There's no need to remove the previous subclass relationships as they are still true in the new setup.