This post is a tricky post,i faced this problem,i had a sharepoint 2007 site,and i want to change its port,to change it do the following :
1) from IIS Manager,right click on the site,and change the port from the old to the new one.
2) From Sharepoint Central Administration,click on operation tab,and click on alternate access mapping (AAM) to map the new url to the created web application url.
For example : you changed the created site from port 9999 to 90 :
http://MyServer:90/ Map To http://myserver:9999/
This tells that if the sharepoint get a request on the port 90 from the iis,map it to the created url web application.
Another Tip :
If you want to change the port which is used from the sharepoint site to connect via SQL Server 2000/2005,simply by using SQL Configuration manager,follow this article:
Hope this helps ...............