Deleting iCloud data
Is it possible to delete old information from my iCloud account in order to free up space?
iPhone 14, iOS 16
If you have iCloud Backups of old devices that you no longer have you can delete them by going (son your current iPhone) to Settings > [username] > iCloud > Manage Account Storage > Backups > [old device name] > Delete Backup.
Also see: Manage your iCloud storage - Apple Support