Of course. You can delete attachment items like any other items, and once you empty the trash and sync, those will stop counting against your online storage space.
I don't have an answer but hop it is alright to hop on the same thread with a few follow up question on this topic, as to not clutter up the forums. Is there a way to see how much space that the files that I currently have are taking up? Can this be viewed by collection/subcollection? Is it possible to see how much space I need to accommodate files that have been added since I surpassed my storage limit? Do bibliographic metadata items themselves take up space, or is it mostly the files (PDFs, etc)?
@mikanovd: For now, you can just check the size of the 'storage' folder in your Zotero data directory for a rough estimate (though that will also include files in any group libraries). You can also use some utility for your OS to find large files and then delete those within Zotero.
In a future version, we'll make it possible to see storage usage by file within Zotero.
@dstillman Thanks for clarifying this for me! Sounds like a great idea for the future version of Zotero - would that be in a Zotero 7 update, or the very distant future in Zotero 8?
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Is there a way to see how much space that the files that I currently have are taking up? Can this be viewed by collection/subcollection? Is it possible to see how much space I need to accommodate files that have been added since I surpassed my storage limit?
Do bibliographic metadata items themselves take up space, or is it mostly the files (PDFs, etc)?
In a future version, we'll make it possible to see storage usage by file within Zotero.
Regular items don't take up storage space.