News Manager 3.0 is almost totally backwards compatible with 2.2.4 and later. To upgrade 2.x to 3.0 you just have to uncompress the zipfile and upload/copy its contents (news_manager.php and news_manager folder) to your site's plugins folder, overwriting all existing files. But there are a some changes in this version's default behaviour.

For full backwards compatibility, insert this in your site's gsconfig.php file:

define('NM2COMPAT', true);

And if you don't want that your posts are inserted in your site's sitemap.xml:

define('NMNOSITEMAP', true);

If you prefer, you could also simply upgrade and then change the settings you need:

Excerpts

Since 3.0 automatically generated excerpts don't truncate words.

If you prefer it the old way, enable Custom Settings and enter:
breakWords 1

Also, a "read more" link is appended to end of excerpts (if needed). To disable this, select:
News Manager Settings -> Add "read more" link to excerpts -> No

Page navigation

Since 3.0 the default page navigation is numbered and with previous and next page links, as opposed to the Older/Newer posts used in 2.x, that can be enabked with Custom settting: navOldNew 1

Pagination index

Pagination index (page= or page/ in URL) starts now at 1 instead of 0 by default. This can be changed back to the old way with a this gsconfig.php setting: define('NMFIRSTPAGE',0);

Post title and <title> tag

News Manager 3.0 tries to insert post titles in the <title> tag when in the single-post view, for better SEO.

You shouldn't have issues if you're already using the News Manager Title plugin or if you're using function nm_post_title like this:
<title><?php nm_post_title(...) or ... ?></title>

However you can have trouble with this (duplicate title in the page or in the <title> tag) if:

  1. your theme's template doesn't have a get_header (or get_i18n_header) tag
    or
  2. you use nm_post_title like this: <title><?php nm_post_title(...); ... ?></title> (with a semicolon instead of "or")

To easily fix any of those, enable Custom Settings and enter:
titleTag 0
Another option for case 1 is inserting the get_header tag in your template (before the closing </head>). There are many other plugins that require it anyway.
For case 2, you can make some change to the code in the <title> tag. If you don't know how, ask in the forum support thread.