Updating content to remove it from the front page shows it as being 'New' I am removing content from the front page as it is out dated, but I don't want to un-publish it as it remains valid information.

Unfortunately Drupal then labels the old article as 'New' and put it to the top of the content list, exactly the opposite effect of the one intended.

How can I stop this?
You should "uncheck" the checkbox "promoted to the frontpage" (which is shown when you 'edit' such nodes). That way it will not be shown on the frontpage anymore.