You cannot modify the "from" name unless you change the user extension's name from the service web. For number, you also need to login your account service web (service.ringcentral.com or service.devtest.ringcentral.com), select a user and click the "Outbound Calls/Faxs" and edit the Fax section accordingly.
Using the RingCentral Phone for Desktop, you can dial or receive test calls, send and receive test SMS or Fax messages in your sandbox environment.
Download RingCentral Phone for Desktop:
Tip: switch to the "sandbox mode" before logging in the app:
3 People are following this question.