Once the campaign is been published, you can ONLY edit the TEXT/MESSAGES, the TIMING DELAY and can ADD STEPS.
You CANNOT edit the ACTIONS, ORDER OF THE SEQUENCE OR REMOVE ANY SEQUENCE for any campaign that it is running and already published.
HOW TO EDIT:
From the specific campaign, click the three dots located at the right side of your campaign dashboard then select Edit Sequence.
You can now edit any message or timing from that campaign.
By Adding more steps from your existing campaign, you can scroll down below to see 'Add New Touch'.
Take note that if you decide to change any message or delay timing, it will only affect your leads that haven't gone through that step and moving forward.