Just download the app from the store again. If it is a complete module it will ask you to replace the existing module or create a new one. Otherwise it will only update the app.
you "re"download and "update" all widgets if it is a widget
If it is a module then you DONT WANT TO DELETE THE ORIGINAL (well at least not in most cases). There is a post about the reason why not somewhere. So in most cases you download the version you want and the system will prompt you to "replace" the package.