You may ask why Transhumanism should be considered a religion. Religion is described as: a cultural system of behaviors and practices, world views, sacred texts, holy places, ethics, and societal organisation that relate humanity to what an anthropologist has called “an order of existence“. Different religions may or may not contain various elements, ranging from the “divine“, “sacred things”, “faith“, a “supernatural being or supernatural beings” or “some sort of ultimacy and transcendence that will provide norms and power for the rest of life.”
As you can see it doesn’t always require the belief in a divine being. It can just be a set of behavior, practices, or world views. This definition makes Transhumanism a religion.
Transhumanists in a nutshell believe in transforming themselves by surgery, tattooing, and/or piercing to make themselves into the vision they have of not only what they want to look like but what they want to be able to do. In addition they want to make themselves not only look different but change who they are on the inside by making themselves smarter, live longer, and stronger. Here is some information about where the ideas of Transhumanism got started. (Make sure click the links below the article for more information).
“Fundamental ideas of transhumanism were first advanced in 1923 by the British geneticist J. B. S. Haldane in his essay Daedalus: Science and the Future, which predicted that great benefits would come from applications of advanced sciences to human biology—and that every such advance would first appear to someone as blasphemy or perversion, “indecent and unnatural”. In particular, he was interested in the development of the science of eugenics, ectogenesis (creating and sustaining life in an artificial environment) and the application of genetics to improve human characteristics, such as health and intelligence.” 
Transhumanism has some common aspect with religion. One of the major factors they have in common is a call to a higher purpose. In most religions this is through God or their own thoughts and beliefs to become a better purpose. Where Transhumanists will receive their advancements will be through science and technology. It is really up to the individual to whether it is considered a religion based on the information that you read or the people you ask. I of course am leaning toward the idea of it being a religion.