Can not update subscribe by email plugin

I cannot update subscribe by email plugin. In the plugin page there is no link to 'update automatically' and in WP Updates I can select the plugin and click 'Update Plugin' but nothing happens. I get the details and version history, and extensive installation instructions but no links to update. I really don't want to download and manually install the updates and I only have this one WPMU plugin installed, so don't want to use WPMU dashboard. What to do?