Thanks for your fast reply!
But what I want, is to change the entire sprite and replace it for another one. Because the other sprite have another "effect".
I guess I will explain with more details.
The game is a shooter, and the thing i want, is when my character "collide" with a power-up, the power-up gives me another weapon. That weapon suposed to be stronger. Then all I did is tried to substitute the original sprite with another one (who suposed to have the other gun).
Sorry for my veeery bad english.