How can I delete files from iCloud after I have received the message "iCloud storage is almost full"?

There is a bunch of junk I don't need bogging down my iCloud. I want to delete most of it, so I don't have to upgrade to a bigger storage package. I have followed the instructions online of how to remove the files, but I can't seem to get past the upgrade portion. When I click "Not Now" for the upgrade, it boots me out of the iCloud drive all together. This happens on my iPhone, my iPad and on iCloud.com. Any help would be appreciated.