Navigate to http://www.adobe.com/products/digitaleditions/.
Scroll down the page until you see the option to install the software and click the install button.
The Adobe Digital Editions Downloader begins downloading the install files. After the download is complete, the installer launches automatically.
Click Continue to begin the installation process.
Select the destination for the drive where you want to install Adobe Digital Editions. Digital Editions only installs on the drive where Mac OS 10 is installed. Once you have selected the destination, click Continue.
Click Install to begin the installation process.
Mac OS X asks that you authorize the installation. Enter an administrator account name and password to authorize the installation.