There are three ways to access the Page Columns page:
Select Admin > WebApps in the Navigation pane, and click Pages for a WebApp. Locate the page and click Column Properties.
Navigate to the page in the WebApp where the column property is to be applied. Click the Change Settings menu on the Site Toolbar, select Design then click Column Properties.
Navigate to the page in the WebApp where the column property is to be applied, right-click the column heading, and click Add or Edit (Control Name) if the column property already exists.