Create more storage by deleting
I nearly reached my 300 MB of storage, so I decided to delete some folders and collections in my Zotero. I also emptied the bin immediately. Yet somehow my storage still seems to be at the same number. What can I do? Doesn't Zotero work with creating storage by deleting collections?
https://www.zotero.org/support/kb/storage_quota_and_local_storage
Also, deleting collections does not delete items under them, unless you specifically chose to do that.