Changing Widget Areas and sizes in Responsive theme

Site is https://www.wincpartners.org/

I’m just putting together a new install for some of our promotional material for my organization.

Most of the theme is easily editable – but I would like to change the three widget areas at the bottom to TWO – and make them wider to accommodate the sizes of the embeds I am trying to use. I am aware that I can change the size of the embeds – but figuring out how to edit these widget areas and add new ones is something I want to do anyway.