As @Anonymous advised, there is currently no way to reset / delete all data in the CRM. HubSpot's Customer Support team work with paid Sales Pro and Marketing customers, that said even they cannot bulk delete data in the way that you describe.
In which case I would advise that yes, you should delete your account and start a new one if you want a completely blank/fresh start. Here are instructions on how to delete your account - please note you must have administrator permissions to do so.