Swap the word Membership with Access in the PMPro expiration text.

my_custom_level_expiration_text.php

<?php
/**
 * Swap the word Membership with Access in the PMPro expiration text.
 * Add this through a code snippet or custom plugin. 
 */
function my_custom_level_expiration_text( $expiration_text, $level ) {
	$expiration_text = str_replace( 'Membership', 'Access', $expiration_text );	

	return $expiration_text;
}
add_filter('pmpro_level_expiration_text', 'my_custom_level_expiration_text', 20, 2);