To reduce the size of a PNG image in Photoshop is a rather hidden feature known only to those who believe in flying penguins.
First, before saving your image for web, you must go to Image > Adjustments > Posterize
After that a small window will pop up with your Posterize settings, the more you increase the Posterize levels it will change the image to lower quality. After you are satisfied with the results, save for web.
It’s that simple and the penguins are still not flying…or are they? Can penguins fly???