Click on your account name (usually your email address) in the
upper right corner and select "Account Settings".
Click "Recreate API Credentials", type "DESTROY" and confirm to
create a new set of API credentials.
You will see a new set of API credentials. Copy them to a safe
place, because you will not be able to access the secret key once
you have closed the window.
Use the new set of API credentials for the API.