I have a website. It has more than 30 pages and there is a news page witch is showing every page in side bar so when I'm updating news, I have to change every page one by one. Do you know any proper solution for maintaining a only one page witch is effecting to all pages ?

Thank you

Assuming you have static pages of some sort (HTML?) it would be better to switch to a dynamic site.

In your case is better to use iframe in every page. Such iframe have to show one news page. So, you have to change one page one time.
But this solution from 20 century

Change your site to use some of free CMS with news module