Deleting Products, Sales, Purchase, or any other transactions:
To delete all transactions – check the list of that transaction (for example List Products), in actions there will be an option to Delete it.
Use that to delete any such transactions
Reset all data
The best way to reset all the business data is to use your existing business as a test/dummy business and register a new business.
By registering a new business it will give a fresh start to your business data.