You have to change the Cloudy Mirror into the Cellestial Mirror. Go to the Macalania Woods and look for a mother and a boy standing next to each other. Help them find the boys father by going back to the place where Yuna and Tidus had their "special moment". They will thank you. Then go back to where the mother and boy was standing and look for a glowing path that goes up into the air. Follow it up and talk to the boy at the top. He will upgrade it for you.