thanks very much for the reply
yes a "T"
here are the conditions, verbatim.
"Time/date changes permitted at any time before each flight departure for a change fee of $ 200 or an upgrade fee of $ 200 plus any difference in fare. Changes subject to availability"
I read that as, a fare difference was applicable for an upgrade only.
but I'll bet you're right
in fact the more I read the conditions, the less clear it gets
thanks again