How do I edit (add text, delete sections, etc. ) to a document that I have scanned into Microsoft word word processor?

If you have scanned it in correctly i.e. as text and not as a picture then you should be able to edit all text?

I have done that but still cannot edit. I can add text but not delete scanned text.

It depends on how you scanned it. It sounds like its scanned as an image not as editable text. You need to use an OCR program to change it to editable text. Most scanners come with such a program. Look up OCR in your scanner's Help screens.