Hi there,
If you navigate to Appearance > Widgets in your admin area, you can remove all existing widgets from the Sidebar area on the right. Penscratch will then automatically detect that there are no sidebar widgets and adjust the width of the site’s content accordingly.
If you’d like to keep the sidebar on some pages, then you can assign the “Full Width, No Sidebar” page template to pages you don’t want to display the sidebar on.
To assign a page template: Navigate to the editor for a page and then select from the Template dropdown menu in the Page Attributes module. The Page Attributes module can generally be found to the right hand of the editor. If you can’t see it, select the Screen Options tab in the upper right and then check the option next to Page Attributes to get the module to display.
Let me know how you get on with that! I’ll be happy to help if extra questions come up, too.