For then benefit of inexperienced users:
Go to your applications.
Unnecessary and pointless.
Find iPhoto
Okay.
Find iPhoto library
Pointless as well, and it won't be in your Applications folder. Try your Pictures Foolder.
Copy Library, paste into new folder on desktop.
Remember that this will now double your disk space usage, so check you have enough. It's also a waste of space as it's not even a back up. I have no idea why this person is suggesting this course of action.
Open latest version of iPhoto ( the version you want to use )
Okay, but we could have done that back at step two...
Then import new folder ( copied library ) to iPhoto version you like.
Well you definitely don't want to do that: Never import one Library to another. Every version and thumbnail is imported like a distinct photo, you lose all your Albums, Keywords etc., the link between Original and Previews is destroyed, the non-destructive editing feature is ruined and so on. In summary: it's mess.
You might choose to open it, of course.
In summary this advice is clueless and likely to lead to data loss.
If you want to return to iPhoto it's simple: Launch iPhoto. Done.