Hi andrzej,
Thanks for reaching to us and appreciate your patience.
1. Change colors
+ Header: Navigate to WoodMart > Header builder > edit default header (highlighted star icon) or you can go through admin bar directly https://prnt.sc/Ct9ehRDvvDV9. Click on the settings icon https://prnt.sc/4cc4IdHoxmbU > Style tab and you can change background color https://prnt.sc/LfDrj9a0MqCS
+ Section: Edit page via Elementor, click on Section > Style tab to change color https://prnt.sc/JcRwBWo-XoDQ
2. Change image
That’s possible, I kindly recommend you import Decor demo then with the help of the import functionality of Elementor you can copy the Home page or some specific blocks and move it to the main website, more detail is here: https://elementor.com/help/template-library/
It also saves your time.
Regards,