general and in theory:
edit page.php and remove the code to get the sidebar – something like:
<?php get_sidebar(); ?>
2.
edit header.php and make sure there is the body_class()
in the body tag; something like:
<body <?php body_class(); ?>>
hat will give you a css class of .page
on all pages, which you can use to change the style of the page to fill the space of the gone sidebar.
3.
(this totally depends on the theme you are using)
add a few new styles to style.css of your theme to correct the content width and the post width to fill the new space:
(only as an example:
.page #content { width:100%; }
.page .hentry { width: 100%; }
do not copy/paste this without being sure that it fits the styles of your theme)
if you have started with step 1 and 2, and have a link to the live site where your progress can be seen, and if you are stuck with the css modifications, you could report back with a link to your site.