First, you have to make your workflow inactive in order to delete any step.
You can delete EMAIL and ACTION steps without damaging workflow sequence.
Subscribers who are waiting in the queue to get the email or execute an action will be moved to the next step in the row after deleting an EMAIL or ACTION step.
The particular report page will not be accessible anymore after deleting the EMAIL step.
If you delete a DELAY step, all subscribers who are waiting on that step will be canceled from the workflow.