1. you can remove the blog part (if it is a slug front, but it looks like this is just directory in which the site is installed so it will not be possible to remove it) but you cannot remove the advert part you can only change it to something else, adding the code below in your theme functions.php file will do that
add_action("adverts_post_type", "customize_adverts_post_type", 10, 2);
function customize_adverts_post_type( $args, $type = null ) {
if( $type != "advert" ) {
return $args;
}
if(!isset($args["rewrite"])) {
$args["rewrite"] = array();
}
$args["rewrite"]["slug"] = "classified";
return $args;
}
After doing this change go to wp-admin / Settings / Permalinks panel and click “Save Changes” button this will reset WP router and apply new URLs, this should also help with categories 404 pages.