Select System Preferences from the Apple Menu at the top left of your screen.
Choose Security & Privacy from the System Preferences menu.
Select General from the tabs at the top of the Security & Privacy page.
Click the Lock icon at the bottom left of the window if you cant change the settings.
Enter your administrative username and password and click Unlock
Select Anywhere from list of places to allow downloaded applications from.
A popup window will appear asking you to confirm your selection. Click the Allow From Anywhere button.