Enabling Azure AD Premium and customizing O365 login page

Hi

I was trying to follow this blog post on how to customize Office 365 login page.

http://www.office365tipoftheday.com/2013/12/17/customize-your-office-365-login-page/

I just dont see any way to enable Azure AD Premium and I dont see any "Customize Branding" buttons there anywhere either.

How can I enable AD Premium to find this branding customizing feature?