To change from one form by a means of a series of unique gears, Protocals and cogs. Or Can mean to change to a more powerful form depening on who is transforming. In the case of humans only special teenagers have been the recipiant of such metamoprhisis powers to become the legendary Power rangers. though this is now true of adults as one former ranger has reclaimed the power.
But the originators of Transform are beings from a sector of the galaxy that is occupied by robotic life forms. the most famous of all of those beings being the Cybertronian races of Autobot, Decepticon, Minicon, Omnicon,Maximal, Predacon and Vehicon. Collectivly known as cybertronians but known to one and all as The Transformers.
the most famous Transformers are the original Optimus Prime and Megatron who hail from the colective known to all as G1.
One of the most powerful Rangers is Dr Tommy Oliver