Error after install of mass email sender

I installed the mass email send zip. After the install I recieve the following error. I'm unable to log into the admin page of the site. How can I log into the admin portion of the site and uninstall the plug in?

Fatal error: Call to undefined function is_site_admin() in /home/forhism3/public_html/forum/wp-content/plugins/128115207061/update-notifications.php on line 417