Click the "Safari" menu, choose "Preferences"
Make sure you have a Safari window open and active; you will see the "Safari" menu in the top left of your screen. Click it, and then click the "Preferences" item.
Click on the "Security" tab
Close the "Preferences" window
Click the red dot in the top left of the window to close the "Preferences" window and resume web browsing. The next time you load a webpage, your new setting will take effect.