First, you must add a payment method to your account. After logging in to your account, click "Manage Organization" on the left. Then click "Manage Payment Methods." Follow the instructions to add and verify a payment method.
Once you have verified a payment method, click Gateways on the left. Select your Gateway, then click Edit. Uncheck the "Evaluation" checkbox and click Save.
Upgrading will immediately remove the evaluation recordings you hear during test calls, and will not require any reconfiguration of your gateway. All settings you customized during your evaluation will be saved.