413 Request Entity Too Large - File Upload Issue for installing theme in Wordpress

Source: http://www.cyberciti.biz/faq/linux-unix-bsd-nginx-413-request-entity-too-large/

Edit the conf file of nginx:

nano /etc/nginx/nginx.conf

Add a line in the http section:

http {
    client_max_body_size 100M;
}

Doen't use MB it will not work, only the M!

Also do not forget to restart nginx

systemctl restart nginx