Remove URL that no longer exist from the sitemap

Hi, my sitemap links to over 30 files that no longer exist on the server (most of them are images I took down a couple of months ago) – travelersuniverse.com/sitemap_index.xml. How can I remove them from the sitemap? In webmasters tool it says these 404 files are linked to either from the sitemap or the feed or both… Thanks!

https://www.ads-software.com/plugins/wordpress-seo/