1. download this file:
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http://update4.jdownloader.org/nupda...3088a4101c.zip
2. Extract the file, and copy those files in a path for ejample: JDownloader2
3. run Updater.jar
4. Maybe you get an error of java too, I said this because I updated twice JD via .jar in a virtual machine and always get the error.
5. If you get whatever error, delete al files of your path in my example is JDownloader2
6. Copy again the files of the .zip (the file that you downloaded)
7. Run again Updater.jar
8. That's it, all worked fine for me.