Fallout: New Vegas has points where you can improve yourself with cybernetic implants and there are various Super Mutants and Ghouls (humans altered via radiation or mutatgenic viruses) along with robots or brains in jars. Though any transhumanism takes a backseat to the post-apocolyptic setting.
Fallout Equestria is a crossover fanfiction between the Fallout universe and My Little Pony: Friendship is magic. Likewise, thoughts of transhumanism is rather incidental to the post-apocalyptic setting but the protagonist does undergo some changes that result in a prolonged lifespan near the end of the story.
Though for stories where transumanism is more the focus... I can think of Wil McCarthys books, The Collapsium and The Wellstone. These stories take place in a setting where programmable matter and nano-tech fabricators called fax machines have radically altered the world. In particular, the fax machines can copy any object, including the human body and mind, and create copies of it or alter them to remove injuries, disease, or the effects of aging.
The Collapsium series take on immortality via the fax machines is interesting in that pretty much everyone seems to understand that the machine destroys the origional when the object is scanned (which technically means that everyone who goes through a fax dies) but since the fax can transmit the persons data and rebuild them on the other end... even curing all their injuries, making them better in some way, or even making multiple copies who can later be re-integrated into a single person with all their individual memories, then the technology is seen as too useful to really avoid.
As such, people in this society have taken on the term 'immorbid', they can die or suffer grievous injuries, but the technology exists to quickly 'repair' them, or just create an exact copy of that person from a backup. There was one case (I think) where a character fell off the side of a ship and was lost into the depths of space... but they had his backup on file so they just printed out a copy of him and all was considered well. Another time it was revealed that a villain had been hacking into the fax network and making copies of various people (ie, someone would use the network to go from point A to point B, the villain intercepted the signal and created a second copy at point C in his lair while another copy appeared at B thinking it all went as normal) he'd then torture or modify them in ways... including making copies of himself to interrogate or abuse.
Its a rather interesting and slightly morbid take on transhumanism and mind uploading but I found it rather a nice read.
I just watched this, a very pretty version of "don't try to make yourself different, just accept who you are", and I realized that self-directed change in fiction is a worthwhile topic.
What I'm looking for is stories where main characters change themselves in ways which are basically improvements-- getting beyond the usual human is a plus, but for purposes of this discussion I'm including any significant positive change.
Another big plus would be the character needing to learn which of their goals make sense, and which methods work.
**ETA:** That was a bit of a stub-- HPMOR is partly about Harry and Hermione changing themselves, generally for the better I think (I've only read it once). It would be interesting to see what happens if Quirrell decides he needs to upgrade himself.
*Stranger in a Strange Land* is an interesting partial example-- the Martian language is presumably an upgrade for the human race, but it was developed by and for Martians, and needs some modification.
A *lot* of relatively recent fiction has people learning martial arts. I think appearance makeovers (typically for women) have become less common. I don't think there's a lot of fiction about appearance makeovers for men-- *The Stars My Destination* has one, but it's offstage. It wouldn't surprise me if *The Count of Monte Cristo* (frequently referenced with TSMD) has one.