In that case you probably need to edit the path in the registry directly.
Not that I'm very comfortable to give that advice because the registry is the one place where you can easily mess up a complete installation. So either get someone who knows what he's doing or at least triple check everything.
At first I would create a System Restore point
If you remember the old path that'll be easy: (I'll give you an example for RISEN)
then open regedit press CTRL-F and search for the path i.e C:\Program Files\Deep Silver\Risen
You'll probably find several entries like Path, Uninstall_CMD etc.
You have to change those paths to reflect the new location ie D:\Games\Deep Silver\Risen
now keep searching by pressing F3 until no more entries are found.
That should do the trick. Please just be careful not to change anything you don't understand...in that case rather ask again until you're 100% sure you understood this right.
-DG