my-pmpro-change-memberlite-register-wording.php

<?php
/**
 * Change the wording of the Register link for the MemberLite theme.
 *
 * 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 my_change_memberlite_register_wording( $translated_text, $text, $domain ) {
	// only change the wording for the memberlite text domain.
	if ( 'memberlite' !== $domain ) {
		return $translated_text;
	}

	switch( $text ) {
	  case 'Register':
		$translated_text = __( 'Sign Up', 'memberlite' );
		break;
	}
	return $translated_text;
   }
add_filter( 'gettext', 'my_change_memberlite_register_wording', 20, 3 );