All Projects posts https://konstruktion.vamtam.com/projects/ have the same demo header image. You can edit or remove the background image by following the steps below.
To begin, navigate to the Toolbar > Edit with Elementor
Enable the Navigator > Click on the 1-st section > Open the Style tab
Here, you can edit the image
After deleting the image, you can select a new one from "Choose Image"
Or click on "Dynamic Tags" and select Posts > Featured Image (so it gets the post's featured image automatically)
We recommend using the Navigator tool to locate all the page elements quickly.
https://developers.elementor.com/docs/dynamic-tags/
Guide to Vamtam Elementor Builder