Replace the Easy Digital Downloads Show Terms slide down with a Popup Maker popup.

use-popup-for-edd-terms-link.php

<?php

function edd_popup_terms_agreement() {
	if ( edd_get_option( 'show_agree_to_terms', false ) ) {
	  $popup_id = '123';
		$agree_text  = edd_get_option( 'agree_text', '' );
		$agree_label = edd_get_option( 'agree_label', __( 'Agree to Terms?', 'easy-digital-downloads' ) );
?>
		<fieldset id="edd_terms_agreement">
			<div id="edd_terms" style="display:none;">
				<?php
					do_action( 'edd_before_terms' );
					echo wpautop( stripslashes( $agree_text ) );
					do_action( 'edd_after_terms' );
				?>
			</div>
			<div id="edd_show_terms">
				<a href="#" class="edd_popup_terms_links popmake-<?php echo $popup_id; ?>"><?php _e( 'Show Terms', 'easy-digital-downloads' ); ?></a>
			</div>
		</fieldset>
<?php
	}
}
remove_action( 'edd_purchase_form_before_submit', 'edd_terms_agreement' );
add_action( 'edd_purchase_form_before_submit', 'edd_popup_terms_agreement' );