Some users do not want to manage a Newsletter.  Some templates have a form to accept a Newsletter on key pages, but it can be removed.

The Newsletter option is in the HTML for the page where an account is created, and it would need to be removed from that location.

When you view the site through and FTP process, the file is

 /templates/<template_name>/content/create_account.tpl.php

You need to remove the HTML row of the table where the NEWSLETTER content is displayed.  In InventoryStores the change cannot be completed from the main Admin menu, but someone with a little HTML knowledge can remove it.

If you intend to go in and remove this line, you should first make a backup copy of your original create_account.tpl.php file locally on your machine, so that it is easy to revert back in case of any problems.