Hello
I think that you can use the next extension: http://www.woothemes.com/products/woocommerce-checkout-field-editor
Also this tool gives you the possibility to change more.
Greetings.
Another way is to copy the template to your theme and edit it there
from:
\woocommerce\templates\checkout\form-billing.php
to:
\yourtheme\woocommerce\checkout\form-billing.php
and then in the copy of that file in your theme, just find and edit the text in this code
<?php if ( WC()->cart->ship_to_billing_address_only() && WC()->cart->needs_shipping() ) : ?>
<h3><?php _e( 'Billing & Shipping', 'woocommerce' ); ?></h3>
<?php else : ?>
<h3><?php _e( 'Billing Details', 'woocommerce' ); ?></h3>
<?php endif; ?>
Hope this helps!
