Oh no! The trick is, if you can convince your "inner editor" to look the other way for a while, is to make a note (or lots of notes if you need to) of what needs to be changed and continue writing forward as if you had made the change. I once changed the protagonist of a story midstream so to speak as I realized I was telling the wrong guy's story.

Don't delete anything because you never know what you might salvage of it later - if even the phrasing of a sentence.