How to Update Robots.txt File in Wordpress by Yoast Plugin

First you install YOAST SEO plugin in your wordpress site, then login your admin panel and go to>>SEO>>TOOLS>>FileEditor.
then click on create robots.txt and edit the file as you want.



Like this:

User-agent:  *
Disallow: /cgi-bin/
Disallow: /wp-admin/
Disallow: /recommended/
Disallow: /comments/feed/
Disallow: /trackback/
Disallow: /index.php
Disallow: /xmlrpc.php
Disallow: /wp-content/plugins/

then last click save. (remember this.)