Migrating from Dropbox to iCloud Drive

Hi all, I've had a Dropbox account for the past 5 years, but it had become quite expensive, so I've decided to switch to an iCloud Drive account. How do I migrate all my files (about 9000 pics and other docs) to my iCloud Drive? I've searched the web but so far I've only been able to migrate this files that were on my Dropbox local drive, not the vast majority that is on the cloud.

Is there a way to do this without downloading ALL the elements on the hard drive first?

Sorry if I'm not able to be very "technical"!

Thanks for your help!

Cheers from Canada

Manu