You can do this with a few simple steps withou install any addons.

1. Active Developer Mode

2. Create a new Action Server (Settings -> Technical -> Server Actions)
   The new server action assign: 

3. • Name -> Clear Journal Entry Name

   • Model -> Journal Entries (account.move)

   • Action To Do: Update the Records

   • Data To Write: Add one line with:

   • • Number (account.move)

     • Evaluation Type: Value

     • Record: (is disable)

     • Value: /

4. Asume that you already cancel the invoices, and journals entries that you want to delete.
   GO to Accounting -> Accounting -> Journals entries (and remove the filters).

5. Refresh the site (press F5)

6. Select all the journal Entries you want to delete.

7. Select from Action select "Clear Journal Entry Name"
   

8. Select all the journal Entries you want to delete. again

9. Select from Action select "Delete"
   -------------------------------- Recomendation -------------------------------------------------

10. Return to Settings -> Technical -> Server Actions and delete the action whe just created. This must not be accesible at any time, because this action can affect reports and documentations.
    Remember this is an behaivors that is not planned in the good use of Odoo, it must be done with absolutly responsibility of the user.