Hi benedict,
1. Are you talking about the hero image on front page? If so, in the page editor, select the container block, you can remove the background image under the background
tab of toolbar :
https://www.screencast.com/t/eEZOTRLR7
For the other page hero images, go to Appearance > elements, there’re 3 block element - page hero
elements (including Global footer ), you can do the same in the element editor.
2. Make sure you’ve assigned a featured image to your posts.
https://wordpress.com/support/featured-images/
3. Make sure you’ve uploaded a logo image at Customizer> Layout > Header > Mobile header.