You can change the number of posts that are shown per page on the Settings → Reading page. Look for the option that says “Blog pages show at most” and set it to “1” so that only one post shows at a time.
Waht I see is a theme with only one full image of the home page and I note that it does not have an excerpts feature. Have you tried going here > Settings > Reading and changing the setting to display only 1 post on the front page? Blog pages show at most 1 posts. That works on free themes.
If it doen’t work then your theme is a premium theme and we Volunteers answering questions on this forum have no knowledge of how they are designed to operate. When you purchased your premium theme what came with that purchase was support directly from the theme designer in the Premium Theme Support Forum. There is a link for the specific Premium Theme support forum under Appearance -> Themes in your blog’s Dashboard