The default search engine in Safari can be changed using the Preferences option. To change the default search engine, click General settings menu available at the top right corner of the browser.
Select Preferences from the available menu list. This would display the following Preferences window as shown below.
In the General tab, navigate to Default search engine and select your preferred search engine from the available drop down values. And click the close button available at the top right corner of the Preferences window.
Now the search engine section in Safari browser should display the changed value as shown below.