Close comments, pingbacks and trackbacks on your posts automatically at intervals set by you
Navigate to Plugins within your WordPress Admin Area
Click "Add new" and in the search box enter "autoclose"
Find the plugin in the list (usually the first result) and click "Install Now"
Download the plugin
Extract the contents of autoclose.zip to wp-content/plugins/ folder. You should get a folder called autoclose.
Activate the Plugin in WP-Admin.
Goto Settings » Auto-Close to configure