1. Go to Settings > Certificates and Key Pairs.
  2. Locate the key you want to set as default.
  3. Click the details icon to expand the appropriate key.
  4. Click the Applications tab.
  5. For the appropriate application, click Reassign.
  6. In the Reassign Key Pair window, select the new key pair.

    If you change the default key, existing applications will continue to use the key that was assigned when the application was created.