That is a support issue. To have your account deleted, post a message in the Free Hosting support forum with the subject "Account deletion request". In the body of the message, include the following form (filled out, of course):
cPanel username:
( ) Inserting an X inside the parentheses signifies that I have made all necessary backups of my free hosting account and will not hold x10Hosting responsible for any data I am unable to recover after my free hosting account is deleted. The X also serves as my digital signature verifying that I have proper authorization to request account deletion of the account specified.
Note that your account will actually be suspended rather than immediately deleted, and will delete itself after 14 days. If you want to immediately delete the account so that you can create a new one, you will have to say so in your account deletion request -- it takes a higher level of access to delete the account than most of the support volunteers have, so your support request would have to be escalated.