I would advise you to rename your old sitemap to sitemap2.xml or something like that and do not update it or delete it, then you can create a new sitemap and only update that one. I am saying this, because deleting a sitemap will have a very negative effect in search engine visibility, if that sitemap is big (over 100 links indexed). Creating a new sitemap will leave the indexed links in your old sitemap "untouched" and you will not have to put extra effort in the new sitemap to get the old links indexed again.