You would need to make a child theme. Once you have that in place, locate header.php in the main theme and copy it into your child theme.
https://codex.wordpress.org/Child_Themes
Once that’s done, find the anchor tag in header.php and remove it.
<a href="<?php echo esc_url( home_url( '/' ) ); ?>" rel="home"> and </a>
If you’re using a text editor, the lines you need to remove are 90 and 92.
thanks, I’m not sure I want to get into the child theme stuff. I don’t want my website to cost to much time and labour Child-themes seem to complicate stuff for me.
Any change tot remove the link without the child-theme?
You could try the using a plugin that enables inserting javascript. A quick search brought shows this plugin:
https://wordpress.org/plugins/css-javascript-toolbox/
Once that’s installed you would insert the javascript code below. The code below won’t remove the link, but but should prevent the default link behavior.
Be sure to have backups in place. If the plugin you choose is coded poorly, there’s a chance you could lose access to your site.
document.getElementsByClassName('header-image').getElementsByTagName('a').addEventListener('click', function(e){
e.preventDefault();
});