How to Transfer iPhoto Library to an External Hard Drive
Backing up your photo library on your Mac is a good idea because it frees up space on the hard drive and allows you to keep more photos in the iPhoto program. One of the best ways to do this is to save the photo library to an external hard drive. You don't need to know much about computers to connect an external drive to your computer and save data to it.
Connect your external hard drive to your computer via the included USB cable and turn on the drive.
Open the "Finder" on your computer's desktop by clicking on the square blue icon of a smiling face in the dock. Click "File" in the top left corner of the desktop and select "New Finder Window" from the list of options to open a duplicate "Finder" window. Place the two windows next to each other.
Click on the "Home" icon in one of the finder windows and select the "Pictures" folder.
Select your external hard drive from the other "Finder" window. The drive icon will be orange.
Click on the "Pictures" folder from the first window and drag and drop it into the drive icon in the other folder. A progress bar will show you how much time it will take to transfer all the data.