How do I change ID to a custom one? How can I change the view block ID from block-views-portfolio-view-block to portfolio?
Add this to your theme's template.php file:

function THEME_preprocess_block(&amp;$variables) {
  if ($variables['block_html_id'] == "block-views-portfolio-view-block")
    $variables['block_html_id'] = "portfolio";

}