I push a button on the stage to display information. Unfortunately the information sometimes is displayed underneath items on the stages. How do I guarantee, when I click a button it's information will be in the forefront.
Make sure the information is in a movieclip. So you should have your main timeline (I'm guessing), a movieclip on that main timeline and inside of the movieclip, the textfield to which you are writing the info.
I'm not sure how you are adding this movieclip/textfield, through actionscript or via the Flash UI, but you should use Actionscript to make sure the movieclip is on top.
Use the swapDepths method to position your movieclip over any other element on the stage, like so:
If you're adding movieclips dynamically afterwards, use some sort of eventhandler to check when the highest depth increases.