Insert module inserts image twice?
You just need to go to the "Manage Display" admin page for your content type (e.g. http://mysite.com/admin/structure/types/manage/article/fields for the 'article' content type).

There you can hide/reorder all of the fields in your content type.

I would guess that currently you have a display field that's aggregating the "Image" field inside of it, and that you also have the "Image" field itself set to display. This would account for the same image being displayed twice.