The control panel you are using is hard coded to show port 80 but has now been replaced with a much better version.
You can now use the version 3 control panel found in the xampp installation folder:xampp-control-3-beta.exe
Right click on it to select to run as an admin for best results.
Click on Exit in the older 2.5 version before starting this version 3 control panel.
The better and latest Control Panel Version3 download is linked in my signature.
Simply extract all the files from the archive to the xampp installation folder and overwrite when asked.
Then right click the exe file to run as administrator and to create a shortcut to the desktop, for example, for easier access.
Make sure that you have exited all other control panel versions before starting this latest version.
Remember when you change the port to 80 you also have to add that to every url you type in your browser, for example:http://localhost:80/index.php
Why do you want to change the default Apache web server port from port 80?