The Django admin generally allows you to select all items by clicking on the select box for the model at the top. Then you can delete them.
Caveats:
- You'd probably want to then de-select any admin users, or at least one that you have access to.
- I would test one deletion first, with a test user that you use to upload a small test file, to see what happens to any uploaded files that get orphaned.
- If/when you do batch-delete, pay attention to the dialog you'll get before completing it. There may be other cascade effects you don't want.
I'd check, but I no longer have access to a live Panda instance.