The plug in you'll need depends on what Internet browser you are using. For Firefox, which is what I use, its a Java Plug In. Usually updating your version of Java will allow you to use the uploader. I've had to do that in the past so I personally know that works.
If you are using IE, then you need some other plug in, I believe it's called Active X. Not sure where you get it though since I don't use IE. Might want to contact support for that info or maybe another community member who uses IE can chime in.
Hope that helps!