If both email addresses use the same email inbox, you can change the sending email address through our email settings. From there you can change the alias as long as its registered through Gmail. Make sure you've also activated a campaign at least once.
You'll also want to make sure that the email you've set as the alias is set up to receive replies to ensure that it recognize when contacts reply to your Interseller sequences.
If both email addresses use different inboxes, you'll need to create a new Interseller account. We cannot migrate the data over because it is tied to your email account and moving that data will cause problems with your email system (Gmail, Outlook, etc). We can, however, move your subscription over without requiring you to re-subscribe. You can also request a CSV of all your contacts by contacting our team for it.