Source Article: https://www.macworld.com/article/2010911/how-to-free-up-icloud-storage-space.html#tk.rss_all
When Apple introduced iCloud in 2011, it announced that every customer with an Apple ID would receive 5GB of iCloud storage space for free. You can add more storage: 50GB ($1 per month; 200GB ($3 per month); 1TB ($10 per month); or 2TB ($20 per month). But if you’re not interested in ponying up extra cash for iCloud storage, that 5GB can quickly get tight.
That’s especially true if you use your iCloud storage allotment to back up your iOS devices. You may find that you’re unable to back up both an iPad and iPhone to iCloud, because you don’t have enough room. Does that mean you need to either pay for more storage or revert to old-fashioned iTunes backups?
