Apple is notoriously stingy with iCloud storage. You get 5 GB per account, no matter how many devices you have. You may own an iPhone and an iPad, and want to back them both up, but, if you have a lot of photos, for example, you may not be able to do so. In which case, you pony up a buck a month to increase your storage to 50 GB.
But you may still want to free up some space on iCloud. There may be apps that you’ve used in the past and no longer use, that take up space. You can do this from the iCloud settings on the Mac, or on iOS.
On the Mac, open System Preferences, click iCloud, then, at the bottom of the pane, next to the storage bar, click Manage. Scroll through the list of apps to find any you no longer use. In some cases, apps only use a tiny amount of storage, such as in the screenshot below, but some apps may store a lot of data in the cloud.
On iOS, you can do the same thing, but it’s a bit harder to get to these settings. Go to the Settings app, then tap your name at the top of the screen. Tap iCloud, then tap the Storage bar, then Manage Storage. You’ll see a list of apps in Documents & Data, but you need to tap Show All to see all the apps that are using your storage.
Tap an app, then tap Edit, then Delete All to remove its data.
You probably don’t need to worry about deleting data from apps that use as little storage as Day One, in the examples above. But you may have abandoned apps that use a lot of storage, so it’s a good idea to delete their data.