Be careful with old versions!
These versions are displayed for reference and testing purposes. You should always use the latest version of an add-on.
Upgrade requires restart (new window) to display buttons, sorry.
The hot upgrade from version 1.9 to 2.1 is not supported.
The hot upgrade from version 1.9 to 2.0 is not supported.
And the both buttons are toggled via a double click.