You can disable a page by going into the advanced tab within the page editor. Simply disabling the page so that it is no longer 'live' on the site will allow you to re-enable the page at a later date if necessary. However, if you would like to permanently delete a page, you can do this by first disabling the page, then right clicking on the page icon in the tree and selecting 'delete page'. You will be asked to confirm this action. Tick the box and then click on the 'Delete page' button and the page will be removed. Please note that this cannot be reversed.