Hello …
1. Jump to the theme’s folder and edit ‘admin/main/options/02.homepage.php’
2. Search lines 154, 155 and 156 and write “full” as image size. As this:
// Set default values for images
$imagesize1 = ‘full’;
$imagesize2 = ‘full’;
$imagesize3 = ‘full’;
3. Save file.
Remember to change this for future theme updates or consider to work with a child-theme.