How to change the location of an updated or newly downloaded App in iTunes?
On windows you can't redirect only these two folders (on OS X and Linux you can) - BUT you can move the whole "iTunes Media" folder to D: then all updates will go there.

In iTunes "Edit > Preferences...->Advanced Section" you can change the location of the media folder - the new folder on D: doesn't need to have the name "iTunes Media", it just need to have the same structure as it had on C:.