That is weird. What location did you download from?
from the link you provided here in this forum.
http://cocos2d-x.org/filedown/CocosCreator_v1.3.1_mac
You are asked to update because you downloaded Creator 1.3.1 and the latest is 1.3.3
Download the update: http://cocos2d-x.org/filedown/CocosCreator_v1.3.3_mac