The first server in a SharePoint farm that runs the SharePoint Products and Technologies Configuration Wizard provisions the SharePoint Central Administration web application and SharePoint configuration database. This Central Administration web application uses the server's name as its host header, and by default a random port number. It also creates a content database for the Central Administration web application, which I previously discussed how to rename.
Using a non-default port adds an extra security layer that follows our defence in depth best practices. Firewalls are more likely to block traffic on these non-default ports, isolating access to SharePoint's Central Administration. In other situations however, it may be desirable to access the Central Administration using friendlier URLs like the default HTTP over port 80, or preferably HTTPS over port 443. One place I like to use default HTTP/HTTPS ports is in my lab so I can follow a simple naming convention like https://spadmin and not have to remember port numbers.
Following are the steps I find work best for me when I want to change the Central Administration web application's port and host header:
I've found it best not to change the Default value in the Alternate Access Mapping from the one SharePoint assigned with the SharePoint Products and Technologies Configuration Wizard as that wizard can experience errors if you have to run it again, like after applying a service pack. Instead leave your custom URL in the intranet mapping field.