Put the Chao you want to evolve into the garden you want to evolve it to ( Dark, Hero, or if you want neutral it doesn't matter). give it 20 to 30 drives of the desired type (red for power, yellow for swim, Green for run or purple for fly). Pet it until it grows round nubs on it's head instead of a point with a hero character if you want a Hero Chao, or pet it with a dark character until the point grows more distinct for a dark Chao, or pet it with both dark and hero characters to keep it even if you want neutral characters. Feed it fruit from the trees until it's stamina is level ten or eleven. Your Chao should evolve right away.