Hidden Documents in iCloud Storage

I am considering to downgrade my iCloud plan to free option (5GB). So I am cleaning up the files in my iCloud storage.

There are 65.45GB documents shown in my storage. However I cannot find them in "Manage Storage". How can I find them and delete them?

Currently I am not able to downgrade because it says I am using more than 5GB of storage. From "Manage Storage", only Mail uses relatively large capacity (418.4MB).

Thanks in advance.