Sorry for the late reply.
Please see here the screenshot with explanations: image. As it is described in the documentation, to edit the slider of a page, you should go to that page back-end. Scroll down the page, to the ‘General Options’ area and select the ‘Slider Options’. In the dropdown, select the slider you want to use. If it is Flexslider, you can add image slides directly from this page. For other sliders (Codeless, Revolution, Layerslider ..etc) you should go to the sliders option panel.
