If your Demo importing failed this is most likely due to your server resources being limited by its configuration - most commonly these are: max_execution_time and memory_limit . If working on a localhost increasing those limits is easy - simply head over to your PHP.ini configuration file, find where those directives are located and increase them to for instance:
max_execution_time = 180
memory_limit = 256M
If you'd rather stay away from your PHP.ini file you can add this code to your 'wp-config.php' file (found in the root of your WP installation) until you manage to import your data, it will also increase your max execution time and memory limits at runtime:
set_time_limit(180); define('WP_MEMORY_LIMIT', '256M');
If none of those work and you are using a hosting somewhere you can always ask them for a quick assistance with this via their Live Chat or Support Phone. It's your right to ask for these updates as you paid for their service and they usually react timely upon similar requests.