Hello,
Alfresco Enterprise releases are announced to partners and customers with active subscriptions via the Support Services of Alfresco. Major releases should also be announced via mails to people who have - at least once - registered contact information with Alfresco, i.e. when signing up for a webinar or downloading of a product data sheet. Additionally, the official forum and blog usually also contain the relevant announcements - so simply subscribing the feeds of these should suffice.
Regards
Axel