Go to WP Menu => Appearance => Customize => Frontpages Section => Slider Section
You Can manage Slider Section title, subtitle and Button.
You Can Change or Manage Title, Subtitle Colors Setting from Customizer.
Go to WP Menu => Appearance => Customize => Frontpages Section => Slider Section
In Content you can see a Upload Image option click on that Upload Image select or drag your image then click on Insert post your image will be post.
