Sitemap Update Regularly?

Hi,
I updated a sitemap to my website few months ago...I added a blog section recently. Should i need to create a new sitemap and upload it to website. I can't see my newly added blog topic to my old sitemap....Does sitemap used to update automatically if we once update? Should we generate and submit new sitemaps if we update new blog articles to websites?

Please help

No need to add a new site map it’ll automatically update

When you refresh your sitemaps periodically, the indexing process is speededed up. Many website owners do not update their sitemaps, even though their websites have been updated. It is not wise not to update the website, as the search engines would not be alerted that any new material has been added to the website and will needs their attention. Thus the new content will be indexed, making it easier for the SERPs than depending on the erratic natural indexing mechanism.

How did you generated the sitemap, Did you used any plugins or manually?