WP Smush.it reduce image file sizes and improve website performance using the Smush.it API within WordPress.
Login to wordpress (wp-admin). In your admin dashboard click plugins and select Add New. Type WP Smush.it in the search field and click Search Plugins button. Install WP Smush.it. After the successfully Installation click the activate Plugin link to activate the plugin.
OR
Download WP Smush.it wordpress plugin. Download link.
Unzip and upload it to your WordPress wp-content/plugins directory.Login to wp-admin. In your admin dashboard click plugins and activate the WP Smush.it wordpress plugin.
Every image you add to a page or post will be automatically run through Smush.it and You don’t have to do anything. For old images click the Smush.it now link in Media Library for each image or run via a bulk Smush option.