You already have a process bound to the HTTP port 80 (Specially after upgrading systems! it will start apache2 by default)
So try this first :
sudo service apache2 stop
sudo systemctl restart nginx
If the problem is not solved then run this command sudo lsof -i:80 to get a list of processes using the port and then stop or disable web server.
Try to stop the process which are using the port 80 using :
sudo fuser -k 80/tcp
sudo systemctl restart nginx
In some cases it may be some issues in the configuration file.
You can use nginx -t -c /etc/nginx/nginx.conf command to find any miss-configuration.
In some cases this error is caused by a default Nginx site already on port 80, removing default config works if you don’t need a default one.
sudo rm /etc/nginx/sites-enabled/default
sudo service nginx restart