Add next page/previous page button

Hi guys,

I’m trying to add a next page/previous page button on my pages. I’ve installed the ‘Next Page, Not Post’ plugin:

http://wordpress.org/extend/plugins/next-page-not-next-post/installation/

It has asked me to copy the following code in my templates:

<?php echo next_page_not_post(); ?>
<?php echo previous_page_not_post(); ?>

I’m assuming this is in my editor –> content-sidebar-page.php, although I’m not entirely sure where I should put this.

The link to my site is:
http://www.sapinfoasap.com/sap-erp/sap-erp-2/

Any help is appreciated, thanks!