If you want to make major changes to your Wordpress site, which requires editing php files, you should use a child theme. It's not difficult to setup, and is well worth the effort.
Being able to have complete control over the design of your theme's styling and functionality is beneficial in the long term.
So, don't be tempted to adjust the style.css or any other .php files in the parent theme, as your changes will be lost whenever the theme is updated.
Don't be frightened over html and css, they are both easy to learn, and of course there's loads of help here at WA as well as elsewhere to learn the basics to get you started. The more you do, the better you'll become!
Let's go and create our child theme...