How to remove the featured image from the top of post?

Hello!

How can I remove the “Featured Image” from the top of post? From all of them.

Unfortunately I’m moving over from a theme, which had it as an option not to have the featured image fixed to the top. So all our posts (and that’s well over 200!) have the post structure as follows:

<h1> header
one or two intro paragraph(s)
featured image

Now all post have the featured image above the headline (which I don’t like anyhow), and then a little down again.

ps: I have already installed a child theme.

[attention: the link provided is only a staging site – I still have a lot of work ahead!]

The page I need help with: [log in to see the link]