To update your Mac, please do the following:
Click on the Apple icon in the top left corner of your screen and click on "Software Update..."
A window will pop up and automatically check for updates
If updates are available, a window will pop up prompting you to install the selected updates; select "Install"
When the updates have been installed, you will see the following screen:
Occasionally, software updates require a system restart. If they do, instad of "Okay" in the above picture, you will see an option to "Install and restart." Select this option and your Mac will automatically log off the current user, install the updates and reboot the computer.