Change a Theme from showing Section Buttons, to Section Groups, which then show all Articles under each Section

I'm using the standard Copenhagen theme, and I unfortunately don't know how to code in HTML.

I'm wondering if anyone would be able to assist me make the following change in Help Centre to change from having Section Buttons, to having Section Groups, which then show all Articles under each Section.

For example, it looks like this at the moment;

But I'd like it to look like this;

Any help would be most appreciated!