Changing modal size

I have a modal that I want the size to be large but when I add the tag


on the button that generates the modal it makes the button large and the modal stays the same size. Also Tried to add the same tag inside the modal like this

<?php $this->beginWidget(


    array(['id' => 'availability-modal',



It returns

Property "TbModal.0" is not defined.

Is there another way to change the modal size?