Hello @tats86,
Thanks for asking. 
You need to use few custom CSS to make necessary changes in headings. I am sharing few sample CSS codes that you can use as a starting point to make required changes. Please add following CSS under X > Launch > Options > CSS:
h1, .h1 {font-size: 400% !important;}
h2, .h2 {font-size: 350% !important;}
h3, .h3 {font-size: 300% !important;}
h4, .h4 {font-size: 250% !important;}
h5, .h5 {font-size: 200% !important;}
h6, .h6 {font-size: 150% !important;}
Another options is to use Cornerstone page builder tools while creating blog posts/pages as it seems that you are using WordPress page editor to create blog posts. It has visual design elements that can be used to create interactive page layouts. In Cornerstone you also get heading elements that can be used to change the heading level and appearance of the same from visual builder. I have created a screencast that you can take a look. https://screencast.com/t/vRiXwyCdK9
Please note that to illustrate my point I have used the example of clasic headline element in the screencast.
In Cornerstone we have released V2 elements and with that you get option to create font templates. Using font templates you can assign the created template in to V2 heading element to further enhance the look and feel of headings.
If you would like to go with custom CSS then I would highly suggest you to take advantage of Google chrome/Firefox dev tools. Using dev tools you can see the changes getting updated in real time within the browser. If you would like to learn more about dev tools, please watch following tutorial.
Thanks.