[xubuntu] software-updater won't show 13.10

I am running xubunto 12.10, and would like to do a dist-upgrade (to 13.04, not 13.10, sorry!). A month ago I was offered the chance to upgrade by the software-manager, but wanted to wait. Now I can't get the system to show me an "upgrade" button at all. I have the option "notify me of new ubuntu" set in the Updates section.

I prefer an upgrade to a clean install, so help appreciated to find a way to do it...Thanks.