I've moved your topic to the Technical Issues section of Magento 1.x as you posted in the Magento 2.x section.
To change your URL to remove /default from it, you will need to:-
1. Change the Base URL in your Magento Admin --> System --> Configurations --> Web --> Unsecure URL & Secure URL.
2. After that, move all your files from your "/default" directory to your domain's root directory and clear all caches.