How to enable:

Discourage search engines from indexing this site

 

First log into the backend of your wordpress.

YourDomain.com/wp-admin

or

YourDomain.com/login

 

The login screen link can change if you are using a plugin or theme that has modified this. The ones listed above are the default logins.

Once logged in you will go to Settings then Reading:

To enable the Discourage search engines from indexing this site, you will need to click the Checkbox, then Save your changes. 

Done!