Just about any change you make to your domain name will first require you to unlock it. Domain locking is provided to ensure that no changes can be made unless you explicitly want to make them.
To unlock your domain name, click the ‘Manage Domains’ tab from within your account dashboard and click the Pencil icon next to the domain name you wish to edit. From here, select the ‘Unlocked’ radio button next to Domain Locking and click Save. Your domain name is now unlocked allowing you to now make changes to it. Don’t forget to lock your domain again by selecting the ‘Locked’ radio button and click save once you are done making the required changes.