Don't freak out, but there's a bit of code the sort through for this tutorial.
Sometimes you get a really great theme, but the font is teeny-tiny, making it hard for visitors to read, and it may even affect CTR or sales. The solution of course is to get a bigger font size, but not all themes allow you to go in an easily change it.
You can definitely change the font size in the Wordpress code, but you need to be brave if you've never done it before.
Luckily, this is one thing that's relatively easy to do if you are patient, and take precautions to prevent total disaster ie breaking your site. Watch this tutorial video, and decide if this is something you want to try.
This is how I first got started customizing my WP themes, and it could be the same for you. Once you figure out where certain bits and pieces are, you can change things to your liking without worrying about being a code-master.
Check it out and tell me what you think.