Now that OS X Mavericks (10.9) is available for all (and for free!), it may be time to upgrade your Mac. When you're ready, upgrading to Mavericks is simple. Just open the App Store and download the upgrade (direct link). Be prepared... the installation file is more than 5 GB in size, so it will take a while to download (actual download time depends on your current Internet connection).
If you have more than one Mac to upgrade in your home or office, downloading the installation file on each Mac can take a very, very long time (as you can imagine). Fortunately, there is a much faster (and just as simple) way to install Mavericks when you have more than one Mac to upgrade.
When you download the free Mavericks installation app from the App Store, it places an app called "Install OS X Mavericks" in your Applications folder then automatically begins the installation.
BEFORE YOUR PROCEED to install Mavericks on your first system, you will want to copy that app to a thumb drive or SD card. If you wait until after the installation, you will find yourself re-downloading the installation app on another computer because Mavericks cleans up after itself (once the upgrade is complete, it will automatically delete the installation app).
Now that you have a copy of the installation app on a USB thumb drive or SD card, you can proceed with the first Mac's installation of Mavericks. When it's time to upgrade other Macs to Mavericks, simply insert your thumb drive or SD card, open Finder and run the "Install OS X Mavericks" app located on the drive. The installation will look exactly as it did on the initial Mac with one difference... you didn't have to download the installation files first.