merging two iPhoto libraries

I have two iPhoto Libraries side by side in my iPhoto picture folder

iPhoto Lib OLD 220 GB (imported from a Mac mini 1.6 10.6.8)

iPhoto Lib 19 GB (already on my Mini 2.53 10.10.2)

I imported the old into my computer and it performed an upgrade, the OLD is now the default .

I want to now merge the two files . However, IMPORT option does not seem to recognise the iPhoto 19 GB . If I look to switch iPhoto from OLD to the 19 GB it wants to repair and says not enough memory (why does it need to repair when the iPhoto 19GB was originally on the computer?).

How do I merge these two files ?