Did you delete your public viz? I can't seem to get to it.
Regardless of that - yes, you should be able to go to public.tableau.com and modify details/description of your viz.
Did that work for you after all?
Sorry all. I think the problem was I had saved a packaged workbook (.twbx file) to my public account, rather than a workbook (.twb file). When I saved the .twb file, I had no problem.