JAS is the PR firm for gasgas - and, unfortunately, their english isn't the best, so i wouldn't expect alot more than google can do with the spanish...
Just glancing through the translated press release. A 4 stroke 515 model will be available and the seat will be wider and softer on all models. Redesigned fuel pump/injection setup allows 1.5 liter greater fuel capacity on 4 stroke. "Battery-less" ignition setup on 4 stroke.