Hero image is fluid/responsive, it is meant for background image (abstract, scenery etc.), it is not designed to place image/banner. DO NOT upload a well-designed image for this area, as it will respond to screen resolution and do not show as a fixed image size.
1- Go to Appearance – Theme Options and select Hero image settings tab
2- Check the box: Enabled Hero Image
3- Optional: Check the box: Show hero image on home page only if you prefer to show the hero image on home page only, instead of all the pages
4- Click Upload to upload your hero image
Note that the recommended image size best fits majority of today’s screen resolution, it is in no way meant to fit into the hero image section as an image/banner placeholder.
5- Insert your hero image caption at Caption content (Sample demo content below video)
6- Optional: Change Caption text color if necessary
7- Click Save settings
Example demo content
<h1>Build a beautiful website that invites sales + subscribers</h1> [button url="http://website.com"]Get Started[/button]