Do you use iTunes? Here's how to get the update.
If you configured iTunes to check for updates automatically (default), you'll be prompted to download and install the update the next time you open iTunes. Or, you can open the program, then click Help - Check for updates. Follow the prompts to finish the installation.
Here's a link to download the current version of iTunes, bundled with QuickTime. If you're using a 64-bit operating system, be sure you install the 64-bit version of iTunes.