https://askubuntu.com/questions/235347/what-is-the-best-way-to-uninstall-nginx

We may want to uninstall and then re-install nginx if any problems occur. First, un-install with code below, then if using a custom nginx, re-install by following the ‘Install Nginx' steps here – WordPress Install (Single Site) – Ubuntu 16.04, NGINX, PHP7

Backup all nginx config files at ‘/etc/nginx' before doing any of this!

Removes all but config files:

$ sudo apt-get remove nginx nginx-common

or remove everything:

$ sudo apt-get purge nginx nginx-common

After using any of the above commands, use this in order to remove dependencies used by nginx which are no longer required:

$ sudo apt-get autoremove