It appears that there is no way to upgrade VCollection version 3 to version 4!
This was confirmed by email from sales staff a few days ago. I find it very hard to believe that there is no current upgrade path at all with this product, yet I have been able to do so with all of my other software products for many years. Apart from the occasional discount offer (last one for VC4 was in May 2015), it seems that we may have to wait until the next one ... whenever that is and sometimes it is not possible for one to upgrade at the times chosen by Arturia.
If any one else knows how a way to upgrade for a reasonable price, then please let me know.