changing port no in tomcat

how do i change the default port no in tomcat.i tried uninstalling and reinstalling the software with the changed port number but it is still not working :disappointed:
when i type the address “http://localhost:8080//” after uninstallation it still displays the Apache Tomcat page saying “If you’re seeing this page via a web browser, it means you’ve setup Tomcat successfully. Congratulations!”.
what is the problem?