mobile applications - taking up lots of room

I have 25G in my mobile apps folder in iTunes [looking at it inside the Finder window]. When I sort by name I find all sorts of what might well be duplicates. Some might be updates or some might be duplicates of others....it's hard for me to know for sure. What can I do to get rid of things that are duplciates? If apps are updated, do they just change the main file or do they come in as different version number? See pictures to illustrate.