The Privacy Settings control who can and cannot view your blog. Please note that these options cannot force Google and other search engines not to search your site.
In WordPress 3.5 this is found under Settings -> General
Pre 3.5, you can change your Privacy Settings via your Settings -> Privacy page:
Site Visibility Options
Here, you will see three Site Visibility options:
Allow search engines to index this site. – This is the setting used by most blogs. It allows everyone to read your blog and enables your blog to be included in search engine results and other content sites.
Ask search engines not to index this site. – If you want all human visitors to be able to read your blog, but want to block web crawlers for search engines, this is the setting for you.
Please note that these options cannot force Google and other search engines not to search your site.