Hey Man! I know this is old, but maybe it’ll help you or someone else. Changing the slider is actually the easy bit!
1) Create a category for your slides. Call it “slideshow” or whatever you’d like.
2) Make a post and name it something like “slide-1” etc. Don’t put anything in the post body! Just set the featured image as the slide you’d like to show! Click the “slideshow” category button, and publish.
3) Go back to Customize theme, and, under Modality Theme Options/Theme Image Slider Settings, you’ll see Image Slider Category. Choose your category “slideshow” from the drop down menu. Save and Publish and et voila; your slideshow works!
