As Andrew mentioned, you can hide that text using CSS only. Placing something like this in your theme's style.css file would do:
p.form-allowed-tags {
display: none;
}If you want it completely removed from the page, code and all, you can edit your theme's comments.php file. Look for comment_form(); (it's near the bottom) and change it to:
comment_form( array( 'comment_notes_after' => '' ) );http://codex.wordpress.org/Function_Reference/comment_form
As for the items in your sidebar, they appear to be normal widgets. You can add/delete/edit them by going to Appearance > Widgets.
https://codex.wordpress.org/WordPress_Widgets
As always, it's recommended to use a child theme if you plan on making edits to the code.