This is a convenient feature of the Mac OS X operating systems. Software Update is found under the blue Apple logo in the far left of the top menu bar. Choose this with your mouse and your Mac will automatically scan Apple’s Web site for newer versions or updates of Apple’s software. Note that Mac OS X 10.5 Leopard can automatically run Software Update checks in the background and let you know when an update is available for your computer. (Many experts recommend not letting your computer do this, as there can be compatibility issues between new OS software and third-party applications.)