It depends. As the guy in above said, things such as weight gain, even something like getting your skin darker or whiter can be achieved nowadays. I mean for God sake people can change their genders and become very convincing women or men (depending on the circumstance, of course). This all possible thanks to technology.
Now, if your thinking about something more deeper or complex (I mean, for instance transforming a 75 years old man into a 13 years old girl)... probably something in the medicine branch, such as a body transplant could allow this someday in the future.
In the 70s Robert J. White a famous doctor performed severals experiments, one of them involving a head transplant in a monkey, he also performed experiments involving a isolated brain (sadly he wasn't able to reconnect the brain in a new body). If you go back further, in the 20s soviet scientists were able to create a dog with two heads.
Recently this news about a Chinese and Italian scientists wanting to performer a "human head transplant" make headlines, you probably heard somewhere.
https://www.businessinsider.com/head-transplant-surgeon-frankenstein-2017-7About much deeper transformations, things that would be physically impossible, such as becoming giants, we could speculate about the possibility of immersive virtual reality allow this sort of thing somewhere down the the line.
A couple years ago there was this very interesting experiments involving VR headsets and simulated body swap.
https://www.polygon.com/2014/3/4/5423330/oculus-rift-vr-gender-swap-girl-mirror-look
Posted: Wed Aug 01, 2018 12:07 pm