1) Navigate to the below file:
"C:\Program Files\Pyramid 2018\config.ini"
Find the line "wwwport=8181" and change it to a port of your choosing.
 

Also update the following line to reflect the new port chosen
[desktop]
startpage=http://localhost:8181

2) Go to the Pyramid repository database and open the following table "[dbo].[server_instances]" and delete the row for the Web Server (see server_description)
 3) Then restart the Pyramid web service as shown below:

4) Once you restart the web service it should re- add the line you deleted but will now have the updated port number. Please note it may take a min or so for the site to come back on line, so please be aware of this.
 

Note that this cannot be used to change to port 80. To do you need to use an external webserver /load balancer. Once such possibility is IIS. To configure IIS please see this article:

https://community.pyramidanalytics.com/t/635fyg/how-to-create-a-pyramid-2018-website-in-iis-after-an-install