how to edit wp category widget

// This alters the get get_terms() arguments and hides some categories
function widget_category_excluder( $args ) {
    // Replace the numbers with category IDs you need hidden
    $args['exclude'] = $args['exclude'].',1,2,3,'; // Keep it safe!
    // Or use exclude_tree to exclude children categories also
    // $args['exclude'] = $args['exclude'].',1,2,3,'; // Keep it safe!
    // (,1,2,3, is enclosed in ',' to ensure digits don't get welded)
    // Test and see what fits your needs best
    return $args;
}
// This allows hooking into WP_Widget_Categories and excluding Terms
add_filter( 'widget_categories_dropdown_args', 'widget_category_excluder' );
add_filter( 'widget_categories_args', 'widget_category_excluder' );

Add this code to your functions.php and experiment. It’s a quick fix. A better alternative is a custom widget with the possibility to hide categories.

Regards.