Thank you all for yr input. Mission achieved. It took a little shifting about so I'll describe in case s/one else wants to increase a Partition.
I used easeus partition master (link above from Vampire Muffin Man).
Step 1. Decrease size of logical drive
" 2. Move new Unallocated space next to Primary Partition (so in my case the
order became C: /Unallocated/ D: ) It would not work when the order was
C:/D:/Unallocated!
" 3. Then easus will allow the increase of C: It's clear in the window how to
achieve this last step.