how to change the opacity of a sprite ? please someone help me!!
Look at the "Modulate" property in the Inspector.
If you want to do it in code:
modulate.a = 0.5
see this https://www.youtube.com/watch?v=LAIaqZl_7c0
If you use modulate it will change the opacity and color of the node and all its children. If you want to change only the modulation of the node you can use selfmodulate. To change opacity you want to modify the alpha channel.