HTH Dialog Developers Group

Depends what you mean by delete.

If it means removing button from Flash File, then find and remove DefineButton instance.

If it means removing button on the run by script, then that button has to have a name identifier. (Name can be assigned in PlaceObject tag instantiating the button for instance placed in Flash file. Script generated objects, buttons included, always have a name.)
You can delete entire button object instance by calling removeMovieClip function on that.
button_name.removeMovieClip();

Or you can just disable button function if you want to keep the button and activate i later. By deleting onRelease or onPress event handler function.
button_name.onRelease = null;

Or you can move the button far outside stage view.
button_name._x = -1000;

Actually you can make button to delete itself on click.
button_name.onRelease = function()
{
   //put button function statements here
  this.removeMovieClip(); //deletes itself, it has to be the last statement in the function, Flash Player won't execute statements after this line.
}