How to replace an iphoto library

Hi there

I would like to replace the iphoto library on my imac with an iphoto library I hold on an external hard drive. However prior to doing this I want to delete some of the rolls of photos as they are duplicated. How/where do I do the deleting and how do I replace the iphoto library on my imac???

thanks in advance
L

First of all, I'd use an app like iPhoto Library Manager to "merge" the twolibraries. That way, you won't inadvertently delete a photo that does not exist on the other library. Then, move the library like this: iPhoto 8.0 Help: Moving your iPhoto Library folder to a new location