@Sandra: At least, you should have post in your site site URL and let me know the elements that you want to hide it so that I can guide you. For now I can just give you example. First, you need to find that page ID. To find id, you can install Catch IDs plugin https://wordpress.org/plugins/catch-ids/. Then you can hide using that page ID. For example, you can see the following css is used to hide page 2 header elements such as Fixed header menu, header, header image and header menu. You can just change that 2 to the page ID that you want and then add it in “Appearance => Theme Options => Custom CSS” box:
.page-id-2 #fixed-header-top,
.page-id-2 #branding,
.page-id-2 #header-image,
.page-id-2 #header-menu {
display: none;
}