Thesis provides a “No Sidebars” template which you can use when you have particular Pages on which you do not wish to display your sidebars.
On the Edit Page subpanel, look for the Attributes section (usually on the right hand side, unless you’re viewing on a small screen).
In the “Template” drop down selector in that section, choose
No Sidebars. Then click the “Update Page” button (or “Publish”, if you’re creating a new page rather than updating an existing one).