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Of course, Apple also gives you a function in iCloud so you can remove the iCloud account from the devices. On the iPhone or iPad, you can do this very quickly in Settings > iCloud by tapping the button Delete Account.
The iCloud account can also be deleted.
After tapping the Delete button, you get a message informing you that all Photo Stream images and documents stored on iCloud are going to be deleted from your device. You need to confirm that you really want to go ahead.
Photo Stream images and documents are deleted from the device.
In the next step, you need to decide what you would like to do with the contacts, calendars, reminders, bookmarks, and notes stored in iCloud. You can either delete these items from your device or keep them. Once you have made your choice, the iCloud account is removed from your device.