Thanks a lot!!!
You need to keep the screenshot.png image.
Activate the child theme then go to Appearance > Editor to edit the style.css file.
Done and seems to be working, I only needed to activate the logo again.
I looks like this now:
Theme Name: Integral Child
Theme URI: http://www.themely.com/themes/integral/
Author URI: http://www.themely.com/
Description: Child theme for Integral (Free Version)
/** Theme customization starts here
Is there a list of settings you can change in the style.css. I want to change some other things too, like the height of the welcome background image on the home page because the picture doesn’t seem to fit.
Do I need to do anything with functions.php ?
Kind regards and thanks a lot again.