Replace "Your Level" with a custom text string using the Gettext filter.

pmpro-change-your-level-text.php

<?php
/**
 * This recipe will change the text Level or Levels to your preferred text.
 *
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */

function gettext_pmpro_your_level_change_text( $output_text, $original_text, $domain ) {
	if ( 'paid-memberships-pro' === $domain ) {
		switch ( $original_text ) {
			case 'Level':
				$output_text = __( 'Membership Plans', 'paid-memberships-pro' ); // change this to whatever you want.
				break;
			case 'Levels':
				$output_text = __( 'Membership Plans', 'paid-memberships-pro' ); // change this to whatever you want.
				break;	
		}
	}
	return $output_text;
}
add_filter( 'gettext', 'gettext_pmpro_your_level_change_text', 20, 3 );