You can change the margins on any page and widen your content area by going to "⋮" at the top right and change the layout to 'Normal', 'Wide' or 'Full'.
Closing Side-bars
Right-Hand Side
To close the right-hand side menu you can either click the "x" in the top right of the panel
Or click on the current panel symbol in the top right corner.
Left-Hand Side
To collapse the left-hand side, use the collapse button in the top left next to the workspace menu.