Increase the memory limit of your server to support delivery of large downloads.
<?php
/**
 * Plugin Name: Easy Digital Downloads - Increase Memory Limit During Download Delivery
 * Description: Increase the memory limit of your server to support delivery of large downloads.
 * Author: NateWr
 * Author URI: https://github.com/NateWr
 * Version: 1.0
 */

if ( ! defined( 'ABSPATH' ) ) exit;

// Increase memory limit during regular download processes
if ( !function_exists( 'eddiml_increase_memory_limit' ) ) {
function eddiml_increase_memory_limit( $download, $email, $payment ) {

	@ini_set( 'memory_limit', '256M' );

}
add_action( 'edd_process_verified_download', 'eddiml_increase_memory_limit', 10, 3 );
} // endif

// Increase memory limit during Software Licensing's API-based updates
if ( !function_exists( 'eddsliml_increase_memory_limit' ) ) {
function eddsliml_increase_memory_limit() {

	@ini_set( 'memory_limit', '256M' );

}
add_action( 'edd_sl_before_package_download', 'eddsliml_increase_memory_limit' );
} // endif
To implement this snippet on your site, create a brand new, empty WordPress plugin and paste the above code inside.