I can't see the changes that 1-Click WP SEO makes in my post
1-Click WP SEO uses "smart filtering" to optimize your posts and pages on the fly. This means that when you go to "edit" a post or page, the optimization will NOT be visible in the editor. But it WILL be visible when you "view post" or when a visitor comes to your website.
This is done so that the "core" of the post stays intact - this will allow you to make any changes you want to the post later very easily (for example, edit your post or choose to optimize it for a different keyword). The SEO isn't "hardcoded", like with other plugins that keep your posts "hostage."
Also, if an SEO factor is already satisfied on the entire page (not just the content area), then the plugin will not add it again. For example, if the navigation menu has a link to the page itself, the plugin will not add a second link.