Transhumanists vs. Extropians vs. Next Level Humans
The World Transhumanist Association seems to be a more general organisation containing persons from the full spectrum of the ideological world. Currently there is a move on by the more socialist cliques to purge the organisation of the more libertarian members. I doubt that this movement will succeed, given the general independence of mind among most people drawn to transhumanism. Extropians apparently contain more libertarians, and focus on technological "fixes," including consciousness downloading and technological augments.
Both of these groups help to draw public attention to the need for continued human evolutionary growth. They also perform a service by providing forums for people who enjoy talking about such ideas, without actually having to get their hands dirty doing anything. Those who cannot do, talk. These people need a place to go to talk.
To the extent that any members of these groups actually accomplish anything, these particular members form subsets of the superset of next level humans. Next level humans are humans who embrace their humanity while having the courage to become more. Courage is more than talking, more than writing a book or teaching a class. Courage is willingness to lead into unknown territory.
A next level human cannot really be a socialist or a libertarian. Those ideologies are suited for between level existence. Both make false promises, lacking the substance to fulfill them.
Next level humans accept technological change, make use of the changes, and often create the innovations that allow further change. Next level humans focus on evolving humanity, however, not technology. Next level humans do not waste time on lines of research that have been seen to be blind alleys. Certainly the focus is on life extension and intelligence increase. Those are necessary, but not sufficient, foundations for next level existence. Between levels may very well achieve both of those ends, and still crash their civilisation.
Next levels will live longer and be more intelligent. They will focus on passing the gains on to the next generation. Between level humans focus on material prosperity and "power", and try to pass these things on to their progeny. Next level humans see prosperity and power as mere means to accomplishing further evolutionary growth. It is the growth that next levels wish to pass on to all humans, not simply their own offspring or clan.
If you want to know transhumanists or extropians, you can easily join one of their organisations. Getting to know potential next level humans will be more difficult. Probably the first step is becoming one yourself.