that doesn’t look like it was built with GeneratePress(?). If so i can’t really advise how to make changes.
Recommended paragraph widths is 45 – 70 characters per line. Your current page fits that recommendation. You could reduce the container a little in width to 700 – 760px. This would give you around 45 characters per line.
I would look at increasing the body text line height to 1.5em which would 24px. And i would increase the Paragraph bottom margin to at least 16px to open up the text a little more.