Messages backed up in icloud

If I disable and delete messages backed up to iCloud, does this also delete the remaining messages, the ones that I want to keep, from my devices? I have run out of space (my free 5GB). I don’t want to pay for additional space, I just want to clear old, unwanted messages from iCloud. I have deleted unwanted messages from my devices, yet I do not have any additional space open up on iCloud.