If you have a site in your account that you no longer need, you can easily delete it. Please be sure you want to do this, as once a site is deleted there is no way to recover it!
For further information on how to delete your site, please read this tutorial: Deleting your website
To create a new website, there are two options available to you:
Option 1: On your My Yola page, click Add New Site button on the top of the page.
Option 2: In the Sitebuilder, go to Menu > Sites. Click Add a new site at the bottom of the page.
You may also find this useful:
How can I delete a file in File Manager?