Safari comes packaged with the operating system on your Apple device. This means that you'll need to update your device in order to update Safari.
Check that your are connected to the internet
Click on the (apple) icon in the very top left hand corner of your screen
Select 'About This Mac'
Click the 'Software Update...' button
If an update is available, follow the steps to update your Mac!
From your home screen, click on 'Settings'.
From the settings menu, select 'General'
Select 'Software Update'
If an update is available, follow the directions to update your device!