How do I upgrade from Express Checkout to Braintree Direct?
If you want to upgrade to full Braintree Direct processing, just apply for a Braintree account.
You'll have to slightly modify the Braintree SDK (formerly v.zero SDK) integrations, based on instructions on http://www.braintreepayments.com, and use the Production API Keys. You can link your PayPal account using the Braintree Control Panel.
To view a demo or download code samples of Braintree or PayPal, visit the PayPal Demo Portal.