Go to PayPal Developer Console and Login to your account after clicking the Log into Dashboard button

Go to REST API apps section and click the Create App button.

Add your own details for the new app and create it.

Switch to Live by clicking the button near your new App's Name.

Copy the Client ID and Secret

Go to your Admin Panel -> Settings -> Payments Tab and enter the Client ID and Secret keys on the paypal section.

Make sure to also switch the Mode to Live and Submit the new settings.