brand new and my site crashed

sorry if I repeat myself but I've only been a paid member for about 30 minutes

I'm not sure which plugin I was installing. It crashed my site with the following error message -- how do I fix?

Fatal error: Cannot redeclare class URI_Template_Parser in /home/content/55/9112755/html/carpalrx-restart/wp-content/plugins/wpmu-dev-plusone/lib/external/google/external/URITemplateParser.php on line 30

UPDATE -- I went in thru ftp and uninstalled dev-plusone plugin and site is back up --