Go to the Mac App Store to upgrade your Mac to OS X Mountain Lion. There are over 200 new features in OS X 10.8. To see if your Mac can support this new OS, check the Technical Specs found here.
$19.99 is a really good price for an OS upgrade (especially if you consider that Microsoft generally charges over $100 for a new Windows operating system).
My wife has a MacBook Pro, so let's see how it runs after we upgrade to Mountain Lion!