Like Nixwebo said, you can open the html file with a text editor, change the html tags, re-save it as .html and upload it to the server again.
Also, another way you can do it, and this is useful if you are working on your website from multiple computers:
Open the web page in your browser... in Windows, you can right click on your mouse anywhere in the page (not sure if this works in Mac, but I am sure there is something equivalent), and click on "View Source Code". Copy the source code and paste it into a text file, edit, and re-save it as a .html file, and upload it again to the server.
Hope I am not causing confusion
Sherif