Is there a way to know what is of all my GO, textures, sounds, etc, are not in use in all scenes, to delete it? When i tested my game, I have inserted some textures, sounds, GO etc and some of them are not in use. I'm using Unity 5.1.1.
When Unity builds the executable, it does so only with required assets. Anything else that might exist in your scenes or projects is simply ignored.
This answer over on Unity Answers has more info.
There are also options available in the Asset Store, such as this one.
Asset Hunter is a tool that analyzes your buildlog and gives you an easily understandable overview over unused assets in your project folder. The results are grouped into folders and file types, making it easy to start cleaning up your project.