Import from Lr 4 classic to Lr Cloud

Hi everyone!

A question that may be trivial but it's giving me quite a bit of headache. 

A bit of background: I have a desktop version of Lr 4, which I received for free when I bought a Leica ages ago. All my pictures are organized in folders on my Mac (quite dated MacBook Pro) and synched with Lr 4. I also have - on Lr 4 - several pictures that I edited on the way, with the usual adjustments of white balancing, tone, cropping, exposure etc. 

I just bought the subscription model with the new Lr. I open the desktop version and it asks to synch an existing Lr catalogue. I select mine and it says it's not supported (only Lr 6 apparently is). Plus, if I try to add the pictures from my Mac on the Lr desktop version, it duplicates the photos and of course I run out of laptop storage. 

If I try online it's even worse. It prompts me to add photos, but I cannot add the whole Pictures folder in my Mac. It asks me to add them one by one... 

I am clearly missing something here. Any mega expert who can help? 

Thank you!

Alberto