onRelease instead of onPress...Help plz :(

I have some script for a sliding gallery and buttons to move the images. Could some one tell me how to change the function from onPress to onRelease so I can animate the button.

this.onEnterFrame = function(){
if(rewind == true && counter > 0){
counter = counter - 1;
prevFrame();
}
else if (rewind == true && counter < 0)
{
rewind = false;
}
}
next_btn.onPress = function(){
rewind = false;
play();
}
prev_btn.onPress = function(){
rewind = true;
counter = 8;
}

Thanks
Mat