Hey Fodera,
dalecosp is right about the content management system, but you should be able to get something pretty slick going with only a little coding at your end. Since you can jump in and out of PHP within an HTML document (with file extension .php!) modifying your existing pages with a little bit of code would be fairly simple.
As for specifics, it largely depends on how you are storing the data that you want to change. Is it in a database? if so, which one? (MySQL, MS SQL, Oracle etc). If not, are you storing the information in a flat text file or are you not currently storing at all?
Ultimately, this only matters in how you get the information into the PHP script. The actual adding of the information to a certain spot on the page would be as easy as outputting a variable even inline with existing HTML code ( eg. <?php echo $news; ?>)
Send us some specifics or a link to the page you want to make dynamic and we can start helping you with actual code!