Copy vendor/friendsofsymfony/user-bundle/FOS/UserBundle/Resources/views/Registration/register_content.html.twig into app/Resources/FOSUserBundle/views/Registration/register_content.html.twig and make changes like:
vendor/friendsofsymfony/user-bundle/FOS/UserBundle/Resources/views/Registration/register_content.html.twig
<form action="{{ path('fos_user_registration_register') }}" {{ form_enctype(form) }} method="POST" class="fos_user_registration_register">
{{ form_widget(form) }}
<div>
<input type="submit" value="{{ 'registration.submit'|trans({}, 'FOSUserBundle') }}" />
</div>
</form>
app/Resources/FOSUserBundle/views/Registration/register_content.html.twig
<form action="{{ path('fos_user_registration_register') }}" {{ form_enctype(form) }} method="POST" class="fos_user_registration_register">
{{ form_start(form) }}
{{ form_errors(form) }}
{{ form_widget(form.email) }}
{{ form_widget(form.name) }}
{{ form_widget(form.username) }}
{{ form_widget(form.plainPassword.first) }}
{{ form_widget(form.plainPassword.second) }}
{{ form_end(form) }}
<input type="submit" value="{{ 'registration.submit'|trans({}, 'FOSUserBundle') }}" />
</form>