How to delete and unsync your iCloud contacts individually or all at once, from any device

You can delete contacts from iCloud by unsyncing your devices from the cloud, and manually deleting several or all contacts on the iCloud website.

How to sign out of iCloud on all of your devices at once to keep your account secure

To sign out of iCloud on all of your devices at once, you can head to iCloud's website and change your password.