Third Party Logins can be deleted ONLY if you also have a standard Passpack User ID and Passwordcombination. If you do not have these, you can set them up under Account > Set a User ID and Settings > Set a Password. Instructions are here.
To manage your Third Party Logins, go to Account > Associate Another Login from within your Passpack account. Scroll down to the see the list of Third Party Logins that have been previously associated. To the right of each login, you should see an X. Click the X to remove Third Party Login.
This will not delete your Passpack account. It will simply tell Passpack, for example, "I no longer want to use my Facebook account to sign into Passpack."