Mac OS X 10.6: Scheduled Check pane of Software Update preferences
Use the Scheduled Check pane of Software Update preferences to check for updates to your computer’s software manually or schedule when your computer checks for updates.
Click Check Now to immediately check for new and updated versions of your computer’s software. When your computer detects that an update is available, you can choose to download and install the update or ignore it.
Check for updates
Select the checkbox to have your computer check for updates automatically, and then choose how often you want to check for updates from the pop-up menu. You can choose to check daily, weekly, or monthly. Your computer will not check for updates if it’s turned off during the time it’s scheduled to automatically check.
Download updates automatically
Select the checkbox to have Software Update download important updates without asking. When the update finishes downloading, you will be notified that it’s ready to be installed.
When an installation is complete, Software Update will check for updates again. It does this because some updates require that you have installed previous updates.