You are able to change your Caller ID that people will see when you place a call, and you can select from any of your phone numbers that you have in your account.
Simply click on the Caller ID dropdown menu on top of your Dialer on the Web App:
and select the desired number from the Caller IDs list.
Then just place the call and that will be the number people will see when receiving calls from you.
If you want to change the Outbound Caller Name (not the phone number), please check out this article.