We wouldn't recommend changing a campaign that is currently in flight. We would recommend canceling the current campaign that is running and restart it with the new flow.
However, if you do, keep in mind that once you have sent Email #1, Email #2 has been created and scheduled. If you want to change Email #2, you will need to cancel the campaign. If you want to change Email #3, you will be able to edit this since it hasn't been created yet.
Still need help? Click contact support and share with us your questions!