I created the sketch for the robot on a grey layer, using default white brush

Work in progress: here I show the stream of my work, since it's too long, I don't have enough time to explain each step. Basically, I chose suitable part of the image to make different parts of the robot. If it's not fitted, I distort the shape using Free Transform or Warp tool. Beside, Burn and Dodge tools are used to adjust the light and shadow of each piece, and the color of each piece was changed using Hue/Saturation adjustment.

Digital painting was used in the later part to make some details on the robot and to make the smokes.

The overall color, light of the image was adjusted using top layers with Overlay, Soft Light, Color blending modes, then soft brush with appropriate colors were used to adjust.