How can I change the header sizes and spacing format in Product theme to reflect the look of the dem

I have set up so far using Product Theme. I am using the default preset style.

My issue is the heading sizes in the slider are small and the spacing between the header, text and button is also condensed and differs in look from the demo. In addition, can you use paragraphs in the text for the slider? Paragraphs are just running into each other.

The headings for the three content boxes are also small.

I have not been able to find where to amend this. Thank you for any help you can offer me.