How to remove categories from posts

You open a post (see Writing Posts) and on the right in the ‘Categories’ block you can deselect the categories assigned to that specific post.

This does not delete the category, but removes it from that post. If you want to delete categories, you should do that via the ‘Categories’ submenu. However, this deletes the category completely and thus removes it from all posts.

This does not work it only puts it in a categorie named Uncategorized

Why do you want to delete it? To not display categories at all on your website? Then I guess it would be easier to change your theme.

By ‘change your theme’ I mean modifying it.

looks a lot better without it i personally beleive

Some themes use a function to determine whether there is more than one category defined for the blog/website. If not, the categories will not be displayed. An example is the Ryu theme‘s ryu_categorized_blog() function (see inc/template-tags.php). This function is than used in the relevant content.php files (like content.php and content-gallery.php) when checking for categories for the post.