Well,after getting no replies, I checked the Ubuntu documentation web
page (my recommendation to all other new Ubuntu users :-) ) after
getting a hit from a Google search for "Upgrading Ubuntu". There were
detailed instructions there for upgrading from 9.10 to 10.04 LTS - it
worked perfectly.

I guess when all else fails, RTFM. (or maybe "search for the FM, then
RTFM").