Here is the website, if you need to take a look: [ External links are visible to forum administrators only ].

I've recently moved it to https (before only some pages were https). Now that I am making changes to my sitemap, I've read that you have to have both variants of robots.txt and XML-map - for http and https.

Need advice, please!!!

from what I see you have redirect from http to corresponding https URLs, in this case you only need one version of sitemap and robots.txt (on https).