To change the passphrase of your Persistent Storage:

  1. Choose Applications ▸ Tails ▸ Persistent Storage to open the Persistent Storage settings.

  2. Click on the Change Passphrase... button in the left of the title bar.

  3. Enter the current passphrase in the Current Passphrase text box.

  4. Enter your new passphrase in the New Passphrase text box.

  5. Enter your new passphrase again in the Confirm New Passphrase text box.

  6. Click Change.

You can now restart Tails and try to unlock the Persistent Storage with the new passphrase.