How to remove Google from the "Start screen"?

[A Debian User <debian@openmailbox.org>]

First of all, sorry for using the term "Start screen" :P

But when you do a search for applications in a GNOME 3 desktop, two 
buttons appear below the screen: "Wikipedia" and "Google".

Apparently, clicking on either of them will open the browser with a 
Wikipedia or Google search using your search terms.

How do you remove Google and replace it with a search engine of your choice?

Thanks.