Open office cannot be install due security issue

Hello,
I downloaded Office for my MAC and when I want to install the program this error appears and all the time I have to install from Mac App Store. Is there way to change this settings so I can download from another servers ? Why is not working ?
Thank you !

“OpenOffice.org” can’t be opened because it is from an unidentified developer. Your security preferences allow installation of only apps from the Mac App Store and identified developers.
Your security preferences allows installation of only apps from the Mac App Store and identified developers.
Google Chrome downloaded this file today at 6:20 PM from sourceforge.net.
