From your question it sounds as if your updating the HTML file on the server in response to user actions. I'm guessing that's not literally what you meant. If it is, though, there are almost certainly better ways to do what you want to do -- depending on what, exactly, it is.
If you are just showing new information to the user, you will want to use Javascript to update the page's DOM. The easiest way for a beginner to do that would be to start by looking at jQuery tutorials. With Javascript (possibly aided by jQuery) you can easily update the content of any part of your page, without needing to actually change the original HTML file in any way.
If you want the page to be updated for everyone who visits it at a later date, then you need to put the new information in a database, and get the content from the database when you the page is requested or loaded.
It would greatly help if you specified exactly what you were trying to do.