The EDU License is fixed for the version that you bought, after the initial purchase you follow standard upgrade process for Pro 8.5->Pro 10 which is labelled as “Update from Cubase 7 / 7.5 / Pro 8 / 8.5” on the steinberg purchase page.
Basically there’s no price reduction for upgrades even if your initial purchase was the EDU edition, see point 7 here for better explaination:-
After your first upgrade it is the full commercial license that you’ll move to. At this point, it may be wise waiting until version 10.5 in a few months.
And note: This is a user forum, i’m not part of Steinberg in anyway.