At last I've managed to update it and all appears to be working smoothly. I went through the DxO support helpdesk who talked me through it (via email).

I had to manually uninstall the old version and a few .dll files. They also sent me a different set-up download link which seemed much quicker. It all took a few days as I think the helpdesk is located the other side of the World looking at the times the replies were sent.

Anyway, I'm glad I was patient as I do find this software being some of the best.