Just move the entire "iPhoto Library" file to your new destination.
Do not open your iPhoto app during the transfer. It will take long time depends what kind of storage you using.

Once the transfer is done, press and hold Option and launch the iPhoto app. On the menu appear asking where is your library. Click "Other..." then point to your newly moved library. And you are done.

From now on, whenever you want to use the iPhoto be sure the external is mounted.

If you have multiple Library, be sure to name them correctly.

This post has been edited by wei: Jan 3 2018, 02:49 PM