In the newest version of our editor, removing email steps that have already been sent to contacts will prompt a warning. Removing a sent email step will not reset the messaged contacts to receive that email step again.
Alternatives to removing sent steps
Instead of removing the sent email step in the sequence, it's better to add a follow-up email to the sequence or create a new sequence and copy the contacts over to the new sequence. Removing a sent step isn't recommended as it can cause issues with keeping track of which messages have been sent to contacts.