I hope you are well today and thank you for your questions.
How to add logo on top?
Fin information about it on the following page in the section “Header Image (Logo Upload)”
How to reduce size of header?
We have to develop some custom CSS code to achieve it.
Could you please share me the screenshot of header showing how you want it to display so that i can help you to achieve it?
It has default box layout, how it can be change in fixed layout?
The theme content is displayed in fixed layout as displayed here https://colorlib.com/sparkling/ Do you also want to display theme header, slider and footer in box layout as described in the below thread?