To cencel/delete the entries.
1. Install the account_cancel module.
2. Configure every Journal to "Allow Canceling Entries". Editing from Accounting->Configuration->Financial Accounting->Journals->Journals
3. Delete any voucher at Accounting->Journal Entries->Journal Vouchers (First Cancel or Set to draft)
4. Cancel all Journal Entries at Accounting->Journal Entries->Journal Entries making its states Unposted.
5. Unreconsile any item at Accounting->Journal Entries->Journal Items (seleced an run action from the right side panel) and then delete all items.
6. Delete all payment (Customer and Supplier)
7. Delete all Supplier vouchers
8. Delete all Sales Receipes
9. Delete all customer refunds
10. Delete all customer and suppliers Invoices

To delete the invoice you can refer following link's answer number 3

https://www.odoo.com/forum/Help-1/question/How-to-delete-an-invoice-after-validation-20831

Thanks,

Nimesh.