Giving Hand theme overriding form fields.

charitable-functions.php

<?php
add_filter( 'charitable_donation_form_fields', 'givinghand_charitable_donation_form_fields', 10, 2 );

function givinghand_charitable_donation_form_fields( $fields, $object ) {
  $fields['donation_fields']['legend'] = '<h4>'. esc_html__( 'How Much Would you like to Donate?', 'givinghand' ) .'</h4>';
  $fields['user_fields']['legend']     = '<h4>'. esc_html__( 'Billing Information', 'givinghand' ) .'</h4>';
	return $fields;
}