When you update information on your site it does not automatically update instantly in Google’s index. Rather, Google’s index is updated approximately once a month after the Google robots have crawled more than 8 billion web pages.
This process is totally automated, so updated or outdated link submissions are not necessary. Changes to your site’s content will be noted by the next crawl. Due to the volume of sites in the index, it is not possible to manually update pages on an individual basis.
Excerpt taken from Google Webmaster Info