I want to delete a Macbook Air iMessage attachment without deleting it from my iPhone

I'm try to free up space on my Mac Air to download a new Operating System. It appears I create enough space by deleting iMessage attachments on my Mac (which currently synchs in iCloud with my phone). Only I don't want to delete the attachments from my iPhone (as both are synched with iCloud) nor do I want to stop backing up the text of messages from my iPhone. Can I delete only the attachments from iMessage on my Mac and while not deleting the iMessage on my iPhone or without permanently stopping my Mac messages from synching with iCloud?