Upgrading E-Newsletter plugin not working seems to be a .rar file rather than .zip

I am trying to upgrade to the latest version of the e-newsletter plugin and keep receiving the following error:

Unpacking the update…

The package could not be installed. PCLZIP_ERR_BAD_FORMAT (-10) : Unable to find End of Central Dir Record signature

I downloaded the plugin directly from the website and noticed it is a .rar, not a .zip file. Could this be my issue? If so, how can I upgrade my current 1.2.2 installation to 1.2.3?

Thanks
Sharon