Domain lock prevents your domain from being transfered. This is a security feature intended to help protect your domain from "highjackers". If you want to transfer your domain out to another registrar, you must first unlock it. By default, domains registered with Register.ca are automatically locked.
When you click "Update" your changes will take effect immediately. If you choose to unlock your domain name to make changes, we strongly recommend re-locking your domain name once the changes have been made.