Click on the "Apple" menu and select "System Preferences"
In "System Preferences" pane, select "Software Update" underneath the System heading.
Automatic updating can be configured here by using the pull down menu. To run a manual update, click on the "Check Now" button.
Mac OS X will now check for any new software updates. If there are updates for your computer, the following screen should appear. Check the updates you want installed.
Click the "Install" button.
OS X will now confirm that you have administrative rights to the computer you are updating. Enter your log in and password and click OK. All system software and application installs will require this password as well.
Read through the license agreements as they appear and click Agree if you accept the terms outlined in the document.
The updates should now begin the download and install process.
When this is done, OS X may prompt you to restart your computer. Restart your computer when prompted to finish the update process.