Why it doesnt show my newly uploaded image icon when i share my game on facebook? Whats wrong with this?

Why I cant change the image icon of my game? I tried many times to replace my first uploaded icon but still it doesnt work out, ? 

How can I earn money in this site? Does anyone knows?

My project from school is done weheheheh.... My project is a game called Boracay games and Buko Boracay... just enjoy my simple game...