chnage one image to another one acc to first image

 i want to chage the my source image to the final image...

on source there are some parts which are dark one and some are light one so i want to show different part with different color.

please see the link below you will see what is my question

https://docs.google.com/file/d/0ByysgfCH0eyTMlZFdl94Q1J3Qms/edit?usp=sharing