Hello,
To reset your account:
0. Take a
backup of your site.
1. Go to cPanel File Manager, visit the public_html folder, and delete
every file and folder in there except for cgi-bin (although you could probably delete that too). You probably want to enable viewing of hidden files/dotfiles so that you can get rid of files like .htaccess
2. Go into MySQL Databases and delete all databases and database users
3. Go into FTP Accounts and delete all of them
4. Go into Email accounts and delete all of them
5. Delete any addon/parked domains you have
That should reset your account to how it was when you first signed up.