When uninstalling Acymailing does not delete the database tables, so you won't loose any personal information and settings. If you really want to do a clean install you need to delete the database tables manually before installing Acymailing again.
Please note that v5 and v6 each use their own set of database tables. The ones labeled "acymailing" are version 5 and the ones labeled "acym" are version 6.
There is also a easy way to do your final migration. In Configuration->Security you'll find a button to start the v5 data migration. :-)