Site Crashed/Can't Access?

I am not sure which version I’m using because I just tried to instal a plugin and now am unable to access my site.

I’m seeing this error:

Fatal error: Cannot redeclare class Mobile_Detect in /home/content/59/11798559/html/ceceliamecca/wp-content/themes/lemonchili/includes/functions/mobile_detect.php on line 35

Any help is appreciated!