How to change web application port number in sharepoint 2010

1st Way :

1- First open "Centeral Administration" ---> "Manage web applications" then select the site which you want to change the port for it, after that go up left and click the small arrow of delete button it'll open a menu, choose "Remove sharepoint from iis web site".
2- It'll open a popup box, choose your site from the drop-down-menu and choose "Yes" for (delete iis web sites)
3- If you go to your IIS manger you'll not find the site now.
4- Now we need to re-add our site with the new Port. From the same position, choose your site again then go up left and click "Extend" button.
5- Now a new popup window will appear, choose "Create a new iis web site" and add your new "Port".
6- Browse your site.

2nd Way :

1- First open "Centeral Administration" --->  Click Application Management ---> Click Configure Alternate Access Mapping ---> Click the web application you are trying to alter --->  Change the port number by altering the URL and click on Save.
2- Open IIS Manager ---> Select the SharePoint site that corresponds with the web application above  ---> Click Bindings ---> Select the current port ---> click Edit ---> change the port number ---> Save.