How to merge 2 lightroom catalogues (version 4.2)

Hi, 

I just upgraded to the latest (4.2) lightroom version. 

I somehow have 2 different catalogues on my computer. I want to merge them into one (without duplicates). 

HOW?

I've googled for an hour and can only find tutorials on how to do this in lightroom classic by using "Import From Another Catalog" which is not available in 4.2.

Going crazy with frustration, as this should be such a simple step, but no info is available anywhere. 

So, how do I do this? I'm on mac.