How do I disable storing my messages on iCloud?

I try not to use iCloud. I like to back up all my photos and files manually into my external hard drives, so I don't have any use for it. But over the last 2 months, I've been getting bombarded by alerts, e-mails, pop-ups, notifications, and every other possible method to warn me that my iCloud is almost full. I finally checked my iCloud storage, and it says 4.53GB of it is messages. I don't want a cloud backup of my texts. I use iMessage on my iPhone and my Macbook. How do I stop iCloud storing these messages?