First of all, check what ports nginx is currently listening on, you can do that with any of the following commands
netstat -tlpn| grep nginx ss -tlpn| grep nginx
So, you probably found nginx listening to port 443 for SSL connections, and on port 80 for plain http….
On many occasions, you may want other application (Such as varnish or apache) to be listening on port 80, So nginx needs to move to another port, in this example, I am moving it to port 8080
Step 1: Go to sites available, there is the default site, and there are any other sites you added to nginX, open those config files that you will find in /etc/nginx/sites-available, search for 80, and replace it wherever it may occure with 8080 or any port of your choice, restrictions are the following, port numbers under 1024 will requier root privilages (So keep it above 1024), and the maximum port number is 65535, Also port 0 can not be used for http (Relevant to UDP though)