In Invision Community, you set where the sidebar for your community should be displayed: on the right or on the left side. This setting is valid for the entire project and cannot be changed just for some pages.
Unless you have FX Pages installed. Then you can easily switch the sidebar in AdminCP. Even more, you can choose in which database the sidebar should change position.
By the way, you can also select pages that are not built with FX Pages. This setting will apply to every selected page in your community.