How to change the teaser for the front page articles In my site : http://www.indiacustomercare.com  front page(which is not displaying correctly) I want to show 200 words in teaser for each article.
I've changed it in Post Settings but does not work.

What could be the reason?
You need to Edit and Save again the articles to take effect.

I know can be painful if you have hundreds of nodes. If you google about it you will find scripts to do it like this
http://befused.com/drupal/script-update-drupal-teasers

Or use the module retease http://drupal.org/project/retease

I advice you to take a database dump before testing these solutions, just in case.