Don't want to learn Bootstrap classes? Go to Bootstrap builder for busy developers.

Bootstrap class: .modal-xl

<!-- Huge modal -->
<button type="button" class="btn btn-primary" data-toggle="modal" data-target=".bd-example-modal-xl">
  Huge modal
</button>

<div class="modal fade bd-example-modal-xl" tabindex="-1" role="dialog"
     aria-labelledby="myHugeModalLabel" aria-hidden="true">
  <div class="modal-dialog modal-xl">
    <div class="modal-content">
      ...
    </div>
  </div>
</div>

Preview