Now come the moments of truth, where you actually get to perform the upgrade to Mavericks! As previously mentioned, you have two upgrade paths: you can upgrade from Snow Leopard (version 10.6.8) or from Lion or Mountain Lion (check for the latest version of either using Software Update, right before you perform the Mavericks upgrade). You must buy the Mavericks upgrade from the Mac App Store, as Apple says there won’t be any physical media sold.
To get Mavericks:
1. From the Apple menu, choose App Store.
The App Store opens, set to the Featured page.
2. Find Mavericks on the Mac App Store (it will almost certainly be right there on the front Featured page), then click the button with the price.