Write operations are still in beta. Before you can access this feature you need to request access to the beta.
Write operations in the Management API (e.g. create, update, delete, patch) for Web Property, View (Profile), and Goal resources is currently available as a developer preview in limited beta. If you're interested in using these features, request access to the beta.
Update: It takes around 3 weeks to get approved. When you are approved you will receive an email from Google inviting you to join the beta test group.