Once you are logged into SolidCP, click on All Customers link.
In the next screen, you will see the list of all created users. you'll see the default admin user there. Click the username link under website is created.
In the next screen, you will see icons SolidCP. To delete a website, under Web & Applications section click Web Sites icon.
In the next screen, you will see the list of previously created websites. Click on a website you want to delete.
Click on Delete button located at bottom of the page. Click OK when your browser asks for the confirmation on delete operation.