Hi there,
Thanks for writing in! To do that, first head over to Appearance -> Customize -> Layout & Design and then select Content Layout as Content Left, Sidebar Right. This global setting will apply to all pages by default.
Head over to Appearance -> Blog section and set Layout to use Global Content Layout,
Then from individual pages (for example homepage), you can select a preferred layout to have a fullwidth page (https://snag.gy/ywCoqR.jpg).
Hope that helps.