Hello,
i would like to know:
-how to select another button at the bottom or top with joystick or keyboard
-and how to select one button at a time, because sometimes many selected buttons at the same time ,
thank you and have a nice day.
cordially
You should check out the New UI tutorials of Unity. Your keywords are eventsystem, eventtrigger and this Redirecting to latest version of com.unity.ugui 
sry, gotta hurry, so not much time to get into deep about how the UI works.