Hi,
Go to Extensions->Manage->Manage and search for Acymailing. Uninstall those entries thet show you a version starting with "6".
You might want to cnsider to leave version 6 on your site. Both versions each use their own set of database tables, so they can co-exist on a site. This will give you the oppotunity to get familiar with v6. Development for v5 has stopped and Acyba is now fully focussing on v6.
