Which version do you have, Claud40?
In general, upgrades inside and interval [1.5 to 1.6 or 6.4 to 6.5] don't require renewal. Going from 1.7, say to 2.0 would require renewal...
Of course, if your subscription ran out ...say...a week before, the approach SD would probably take would be to upgrade you without renewing...
I can't and am not saying these things in all cases and I don't speak for SD, but why not ask SD sales? They'll be there and answer your question in better detail than I could on Monday...
