Step 1 : Check the default port by accessing the server IP address in the browser .

Step 2:  Login into the server using root credentials through putty .

Step 3: Open Nginx configuration file with a text editor .

Command : 

# vi /etc/nginx/nginx.conf

Press ‘ I ’ for the insert/modification mode .

Step 4: Change the default port of the nginx to the custom port .

Before change : port is 80 as shown below in screetoshot

After change : Port has been changed to 8081 (here) as shown in screenshot .

Step 5 : Restart the nginx and network service .

Command : 

# systemctl status nginx

# systemctl status network

Step 6 : Now check the webserver while accessing the server IP_address:8081  in the browser. 

URL: - http://server_domain_name_or_IP:8081