You can easily delete a website backup from within your cPanel account with Softaculous. To delete a website backup:

1. Log in to your cPanel dashboard

2. Click Softaculous App Installer in the Software section 
   
   

3. Click the Backup icon located in the top right-hand corner of your screen 
   
   

4. Click the red 'X' icon to the right of the backup you would like to delete

You're done!

See also Login URLs You Need to Know, Accessing Your cPanel Account, Make a cPanel Account Backup, Softaculous Overview