/ Uninstall Nginx
sudo apt-get remove nginx
sudo apt purge nginx*

//Then, install Nginx following document: http://nginx.org/en/linux_packages.html#Ubuntu
sudo apt install curl gnupg2 ca-certificates lsb-release
echo «deb http://nginx.org/packages/ubuntu `lsb_release -cs` nginx»| sudo tee /etc/apt/sources.list.d/nginx.list
curl -fsSL https://nginx.org/keys/nginx_signing.key | sudo apt-key add —
sudo apt update
sudo apt install nginx