I have heard that one way that you can upgrade a feature in SharePoint with new files is to do a retract deploy. I believe this is what Visual Studio 2010 does when you do a Deploy. What are the Power Shell commands to-do a retract deploy?
If you are looking for powershell commands to retract\deploy you need this:
But your tags a little bit confusing..
Chris O'Brien have a good topics that describes how to update feature correctly. Also he provided a tool that can help you to do it.