Below is a diagram which lists all of the human race evolutions, once you pick your first evolution you are locked to that race line and can not jump to another race evolution in another line.
To evolve you should seek out an Evolved Spirit NPC, there is one at 32, 62 (Knotwood Valley) inside the South Glade Tower, but there are others.
The rewards listed above are a one time thing applied when you evolve, there are no per level stat bonuses from evolving.