The axes of research and intervention on man are of interest – the manner techno science changes our image and modifies our body. In itself, there is no need to be "posthuman", "transhumanist" or something else to feel like making a genetical test on your embryo, to follow a cellular therapy, operate aesthetical modifications and so forth; yet, it’s this sum of small things in all sorts of domains that people start to create by need or desire that gradually diverge human evolution.
For the sake of answering your question:
Transhuman is a process, a transitional state.
Posthuman is a result.
Etymology suffices to clarify the difference between "trans" and "post": transhumanism aims the improvement of man, whereas posthumanism seeks to surpass it.
The transhuman process position might be aimed towards a clear goal (maybe a posthumanism), or a sort of shifting where we accumulate and test, often with negative and positive restrictions in some directions, typical of pragmatical positions that pretend to be without ideology in adapting the one of the moment.
Obviously, I object this position that pretends to be disideologized and that details very rarely what it means by a certain foundational concept.