fatal error message after downloading plugin

I am not sure if the which version of WP I am using but i think it is 4.2.2 and I cannot access editor or my website due to the fatal error. I have been live for several years and just downloaded the slocum theme modern business to give my website a new look – it recommended that I download a plugin which is did and now i get this fatal error:

Fatal error: Call to undefined function is_customize_preview() in /home/content/01/9334801/html/wp-content/plugins/note/includes/class-note-customizer.php on line 137

I cannot access editor or my website aeconsulting-llc.com
any help is greatly appreciated