How Do I Delete An iCloud Account From My Mac?
Removing an iCloud account from your Mac is a relatively painless process. Go to the Apple menu at the top left of your screen and select System Preferences. Choose the iCloud panel. Then click on "Sign Out" to disable the iCloud account on your Mac.
Warning: If you sign out, any mail, contacts, calendars, photos, notes, reminders, or other documents that are stored in iCloud will be removed from your Mac. They will remain stored in iCloud so you can always get them back by logging back into iCloud.