1. Login to your WordPress admin page.
2. Click on Plugins then Add New.
3. In the search box, type Google Libraries.
4. On the search results page, click Install Now for Google Libraries.
5. Be sure to activate the plugin after it is installed.
Here's the official description of Google Libraries:
This provides numerous potential performance benefits:
increases the chance that a user already has these files cached
takes load off your server
uses compressed versions of the libraries (where available)
Google's servers are set up to negotiate HTTP compression with the requesting browser"
Read more: Ghacks