If you've been working with APEX 5.1 early adopter 1 (EA1) at http://apexea.oracle.com, you should have received notification from Oracle that it will be shutting down soon. As we were told when signing up, there is no way to transfer applications from EA1 into anything else, so there isn't really anything you need to do at this time.
I'm looking forward to early adopter 2 - the interactive grid in APEX 5.1 is a big step forward. For a first impression of it, refer to my Wiki article. There are many features not part of EA1, so I'm eagerly awaiting EA2.